Hi Laurent,
Thanks for your analysis for the last perf results.
Your mentioned ," the major differences at the head of the perf report is the 92% testcase which is weirdly not reported
on the head side", which is a bug of 0-day,and it caused the item is not counted in perf.
I've triggered the test page_fault2 and page_fault3 again only with thread mode of will-it-scale on 0-day (on the same test box,every case tested 3 times).
I checked the perf report have no above mentioned problem.
I have compared them, found some items have difference, such as below case:
page_fault2-thp-always: handle_mm_fault, base: 45.22% head: 29.41%
page_fault3-thp-always: handle_mm_fault, base: 22.95% head: 14.15%
So i attached the perf result in mail again, could your have a look again for checking the difference between base and head commit.
Thanks,
Haiyan, Song
________________________________________
From: owner-linux-mm@xxxxxxxxx [owner-linux-mm@xxxxxxxxx] on behalf of Laurent Dufour [ldufour@xxxxxxxxxxxxxxxxxx]
Sent: Tuesday, July 17, 2018 5:36 PM
To: Song, HaiyanX
Cc: akpm@xxxxxxxxxxxxxxxxxxxx; mhocko@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; kirill@xxxxxxxxxxxxx; ak@xxxxxxxxxxxxxxx; dave@xxxxxxxxxxxx; jack@xxxxxxx; Matthew Wilcox; khandual@xxxxxxxxxxxxxxxxxx; aneesh.kumar@xxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; mpe@xxxxxxxxxxxxxx; paulus@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; hpa@xxxxxxxxx; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@xxxxxxxxx; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; haren@xxxxxxxxxxxxxxxxxx; npiggin@xxxxxxxxx; bsingharora@xxxxxxxxx; paulmck@xxxxxxxxxxxxxxxxxx; Tim Chen; linuxppc-dev@xxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
Subject: Re: [PATCH v11 00/26] Speculative page faults
On 13/07/2018 05:56, Song, HaiyanX wrote:
> Hi Laurent,
Hi Haiyan,
Thanks a lot for sharing this perf reports.
I looked at them closely, and I've to admit that I was not able to found a
major difference between the base and the head report, except that
handle_pte_fault() is no more in-lined in the head one.
As expected, __handle_speculative_fault() is never traced since these tests are
dealing with file mapping, not handled in the speculative way.
When running these test did you seen a major differences in the test's result
between base and head ?
>From the number of cycles counted, the biggest difference is page_fault3 when
run with the THP enabled:
BASE HEAD Delta
page_fault2_base_thp_never 1142252426747 1065866197589 -6.69%
page_fault2_base_THP-Alwasys 1124844374523 1076312228927 -4.31%
page_fault3_base_thp_never 1099387298152 1134118402345 3.16%
page_fault3_base_THP-Always 1059370178101 853985561949 -19.39%
The very weird thing is the difference of the delta cycles reported between
thp never and thp always, because the speculative way is aborted when checking
for the vma->ops field, which is the same in both case, and the thp is never
checked. So there is no code covering differnce, on the speculative path,
between these 2 cases. This leads me to think that there are other interactions
interfering in the measure.
Looking at the perf-profile_page_fault3_*_THP-Always, the major differences at
the head of the perf report is the 92% testcase which is weirdly not reported
on the head side :
92.02% 22.33% page_fault3_processes [.] testcase
92.02% testcase
Then the base reported 37.67% for __do_page_fault() where the head reported
48.41%, but the only difference in this function, between base and head, is the
call to handle_speculative_fault(). But this is a macro checking for the fault
flags, and mm->users and then calling __handle_speculative_fault() if needed.
So this can't explain this difference, except if __handle_speculative_fault()
is inlined in __do_page_fault().
Is this the case on your build ?
Haiyan, do you still have the output of the test to check those numbers too ?
Cheers,
Laurent
> I attached the perf-profile.gz file for case page_fault2 and page_fault3. These files were captured during test the related test case.
> Please help to check on these data if it can help you to find the higher change. Thanks.
>
> File name perf-profile_page_fault2_head_THP-Always.gz, means the perf-profile result get from page_fault2
> tested for head commit (a7a8993bfe3ccb54ad468b9f1799649e4ad1ff12) with THP_always configuration.
>
> Best regards,
> Haiyan Song
>
> ________________________________________
> From: owner-linux-mm@xxxxxxxxx [owner-linux-mm@xxxxxxxxx] on behalf of Laurent Dufour [ldufour@xxxxxxxxxxxxxxxxxx]
> Sent: Thursday, July 12, 2018 1:05 AM
> To: Song, HaiyanX
> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; mhocko@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; kirill@xxxxxxxxxxxxx; ak@xxxxxxxxxxxxxxx; dave@xxxxxxxxxxxx; jack@xxxxxxx; Matthew Wilcox; khandual@xxxxxxxxxxxxxxxxxx; aneesh.kumar@xxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; mpe@xxxxxxxxxxxxxx; paulus@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; hpa@xxxxxxxxx; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@xxxxxxxxx; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; haren@xxxxxxxxxxxxxxxxxx; npiggin@xxxxxxxxx; bsingharora@xxxxxxxxx; paulmck@xxxxxxxxxxxxxxxxxx; Tim Chen; linuxppc-dev@xxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
> Subject: Re: [PATCH v11 00/26] Speculative page faults
>
> Hi Haiyan,
>
> Do you get a chance to capture some performance cycles on your system ?
> I still can't get these numbers on my hardware.
>
> Thanks,
> Laurent.
>
> On 04/07/2018 09:51, Laurent Dufour wrote:
>> On 04/07/2018 05:23, Song, HaiyanX wrote:
>>> Hi Laurent,
>>>
>>>
>>> For the test result on Intel 4s skylake platform (192 CPUs, 768G Memory), the below test cases all were run 3 times.
>>> I check the test results, only page_fault3_thread/enable THP have 6% stddev for head commit, other tests have lower stddev.
>>
>> Repeating the test only 3 times seems a bit too low to me.
>>
>> I'll focus on the higher change for the moment, but I don't have access to such
>> a hardware.
>>
>> Is possible to provide a diff between base and SPF of the performance cycles
>> measured when running page_fault3 and page_fault2 when the 20% change is detected.
>>
>> Please stay focus on the test case process to see exactly where the series is
>> impacting.
>>
>> Thanks,
>> Laurent.
>>
>>>
>>> And I did not find other high variation on test case result.
>>>
>>> a). Enable THP
>>> testcase base stddev change head stddev metric
>>> page_fault3/enable THP 10519 ± 3% -20.5% 8368 ±6% will-it-scale.per_thread_ops
>>> page_fault2/enalbe THP 8281 ± 2% -18.8% 6728 will-it-scale.per_thread_ops
>>> brk1/eanble THP 998475 -2.2% 976893 will-it-scale.per_process_ops
>>> context_switch1/enable THP 223910 -1.3% 220930 will-it-scale.per_process_ops
>>> context_switch1/enable THP 233722 -1.0% 231288 will-it-scale.per_thread_ops
>>>
>>> b). Disable THP
>>> page_fault3/disable THP 10856 -23.1% 8344 will-it-scale.per_thread_ops
>>> page_fault2/disable THP 8147 -18.8% 6613 will-it-scale.per_thread_ops
>>> brk1/disable THP 957 -7.9% 881 will-it-scale.per_thread_ops
>>> context_switch1/disable THP 237006 -2.2% 231907 will-it-scale.per_thread_ops
>>> brk1/disable THP 997317 -2.0% 977778 will-it-scale.per_process_ops
>>> page_fault3/disable THP 467454 -1.8% 459251 will-it-scale.per_process_ops
>>> context_switch1/disable THP 224431 -1.3% 221567 will-it-scale.per_process_ops
>>>
>>>
>>> Best regards,
>>> Haiyan Song
>>> ________________________________________
>>> From: Laurent Dufour [ldufour@xxxxxxxxxxxxxxxxxx]
>>> Sent: Monday, July 02, 2018 4:59 PM
>>> To: Song, HaiyanX
>>> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; mhocko@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; kirill@xxxxxxxxxxxxx; ak@xxxxxxxxxxxxxxx; dave@xxxxxxxxxxxx; jack@xxxxxxx; Matthew Wilcox; khandual@xxxxxxxxxxxxxxxxxx; aneesh.kumar@xxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; mpe@xxxxxxxxxxxxxx; paulus@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; hpa@xxxxxxxxx; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@xxxxxxxxx; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; haren@xxxxxxxxxxxxxxxxxx; npiggin@xxxxxxxxx; bsingharora@xxxxxxxxx; paulmck@xxxxxxxxxxxxxxxxxx; Tim Chen; linuxppc-dev@xxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
>>> Subject: Re: [PATCH v11 00/26] Speculative page faults
>>>
>>> On 11/06/2018 09:49, Song, HaiyanX wrote:
>>>> Hi Laurent,
>>>>
>>>> Regression test for v11 patch serials have been run, some regression is found by LKP-tools (linux kernel performance)
>>>> tested on Intel 4s skylake platform. This time only test the cases which have been run and found regressions on
>>>> V9 patch serials.
>>>>
>>>> The regression result is sorted by the metric will-it-scale.per_thread_ops.
>>>> branch: Laurent-Dufour/Speculative-page-faults/20180520-045126
>>>> commit id:
>>>> head commit : a7a8993bfe3ccb54ad468b9f1799649e4ad1ff12
>>>> base commit : ba98a1cdad71d259a194461b3a61471b49b14df1
>>>> Benchmark: will-it-scale
>>>> Download link: https://github.com/antonblanchard/will-it-scale/tree/master
>>>>
>>>> Metrics:
>>>> will-it-scale.per_process_ops=processes/nr_cpu
>>>> will-it-scale.per_thread_ops=threads/nr_cpu
>>>> test box: lkp-skl-4sp1(nr_cpu=192,memory=768G)
>>>> THP: enable / disable
>>>> nr_task:100%
>>>>
>>>> 1. Regressions:
>>>>
>>>> a). Enable THP
>>>> testcase base change head metric
>>>> page_fault3/enable THP 10519 -20.5% 836 will-it-scale.per_thread_ops
>>>> page_fault2/enalbe THP 8281 -18.8% 6728 will-it-scale.per_thread_ops
>>>> brk1/eanble THP 998475 -2.2% 976893 will-it-scale.per_process_ops
>>>> context_switch1/enable THP 223910 -1.3% 220930 will-it-scale.per_process_ops
>>>> context_switch1/enable THP 233722 -1.0% 231288 will-it-scale.per_thread_ops
>>>>
>>>> b). Disable THP
>>>> page_fault3/disable THP 10856 -23.1% 8344 will-it-scale.per_thread_ops
>>>> page_fault2/disable THP 8147 -18.8% 6613 will-it-scale.per_thread_ops
>>>> brk1/disable THP 957 -7.9% 881 will-it-scale.per_thread_ops
>>>> context_switch1/disable THP 237006 -2.2% 231907 will-it-scale.per_thread_ops
>>>> brk1/disable THP 997317 -2.0% 977778 will-it-scale.per_process_ops
>>>> page_fault3/disable THP 467454 -1.8% 459251 will-it-scale.per_process_ops
>>>> context_switch1/disable THP 224431 -1.3% 221567 will-it-scale.per_process_ops
>>>>
>>>> Notes: for the above values of test result, the higher is better.
>>>
>>> I tried the same tests on my PowerPC victim VM (1024 CPUs, 11TB) and I can't
>>> get reproducible results. The results have huge variation, even on the vanilla
>>> kernel, and I can't state on any changes due to that.
>>>
>>> I tried on smaller node (80 CPUs, 32G), and the tests ran better, but I didn't
>>> measure any changes between the vanilla and the SPF patched ones:
>>>
>>> test THP enabled 4.17.0-rc4-mm1 spf delta
>>> page_fault3_threads 2697.7 2683.5 -0.53%
>>> page_fault2_threads 170660.6 169574.1 -0.64%
>>> context_switch1_threads 6915269.2 6877507.3 -0.55%
>>> context_switch1_processes 6478076.2 6529493.5 0.79%
>>> brk1 243391.2 238527.5 -2.00%
>>>
>>> Tests were run 10 times, no high variation detected.
>>>
>>> Did you see high variation on your side ? How many times the test were run to
>>> compute the average values ?
>>>
>>> Thanks,
>>> Laurent.
>>>
>>>
>>>>
>>>> 2. Improvement: not found improvement based on the selected test cases.
>>>>
>>>>
>>>> Best regards
>>>> Haiyan Song
>>>> ________________________________________
>>>> From: owner-linux-mm@xxxxxxxxx [owner-linux-mm@xxxxxxxxx] on behalf of Laurent Dufour [ldufour@xxxxxxxxxxxxxxxxxx]
>>>> Sent: Monday, May 28, 2018 4:54 PM
>>>> To: Song, HaiyanX
>>>> Cc: akpm@xxxxxxxxxxxxxxxxxxxx; mhocko@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; kirill@xxxxxxxxxxxxx; ak@xxxxxxxxxxxxxxx; dave@xxxxxxxxxxxx; jack@xxxxxxx; Matthew Wilcox; khandual@xxxxxxxxxxxxxxxxxx; aneesh.kumar@xxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; mpe@xxxxxxxxxxxxxx; paulus@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; hpa@xxxxxxxxx; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@xxxxxxxxx; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi; linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; haren@xxxxxxxxxxxxxxxxxx; npiggin@xxxxxxxxx; bsingharora@xxxxxxxxx; paulmck@xxxxxxxxxxxxxxxxxx; Tim Chen; linuxppc-dev@xxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
>>>> Subject: Re: [PATCH v11 00/26] Speculative page faults
>>>>
>>>> On 28/05/2018 10:22, Haiyan Song wrote:
>>>>> Hi Laurent,
>>>>>
>>>>> Yes, these tests are done on V9 patch.
>>>>
>>>> Do you plan to give this V11 a run ?
>>>>
>>>>>
>>>>>
>>>>> Best regards,
>>>>> Haiyan Song
>>>>>
>>>>> On Mon, May 28, 2018 at 09:51:34AM +0200, Laurent Dufour wrote:
>>>>>> On 28/05/2018 07:23, Song, HaiyanX wrote:
>>>>>>>
>>>>>>> Some regression and improvements is found by LKP-tools(linux kernel performance) on V9 patch series
>>>>>>> tested on Intel 4s Skylake platform.
>>>>>>
>>>>>> Hi,
>>>>>>
>>>>>> Thanks for reporting this benchmark results, but you mentioned the "V9 patch
>>>>>> series" while responding to the v11 header series...
>>>>>> Were these tests done on v9 or v11 ?
>>>>>>
>>>>>> Cheers,
>>>>>> Laurent.
>>>>>>
>>>>>>>
>>>>>>> The regression result is sorted by the metric will-it-scale.per_thread_ops.
>>>>>>> Branch: Laurent-Dufour/Speculative-page-faults/20180316-151833 (V9 patch series)
>>>>>>> Commit id:
>>>>>>> base commit: d55f34411b1b126429a823d06c3124c16283231f
>>>>>>> head commit: 0355322b3577eeab7669066df42c550a56801110
>>>>>>> Benchmark suite: will-it-scale
>>>>>>> Download link:
>>>>>>> https://github.com/antonblanchard/will-it-scale/tree/master/tests
>>>>>>> Metrics:
>>>>>>> will-it-scale.per_process_ops=processes/nr_cpu
>>>>>>> will-it-scale.per_thread_ops=threads/nr_cpu
>>>>>>> test box: lkp-skl-4sp1(nr_cpu=192,memory=768G)
>>>>>>> THP: enable / disable
>>>>>>> nr_task: 100%
>>>>>>>
>>>>>>> 1. Regressions:
>>>>>>> a) THP enabled:
>>>>>>> testcase base change head metric
>>>>>>> page_fault3/ enable THP 10092 -17.5% 8323 will-it-scale.per_thread_ops
>>>>>>> page_fault2/ enable THP 8300 -17.2% 6869 will-it-scale.per_thread_ops
>>>>>>> brk1/ enable THP 957.67 -7.6% 885 will-it-scale.per_thread_ops
>>>>>>> page_fault3/ enable THP 172821 -5.3% 163692 will-it-scale.per_process_ops
>>>>>>> signal1/ enable THP 9125 -3.2% 8834 will-it-scale.per_process_ops
>>>>>>>
>>>>>>> b) THP disabled:
>>>>>>> testcase base change head metric
>>>>>>> page_fault3/ disable THP 10107 -19.1% 8180 will-it-scale.per_thread_ops
>>>>>>> page_fault2/ disable THP 8432 -17.8% 6931 will-it-scale.per_thread_ops
>>>>>>> context_switch1/ disable THP 215389 -6.8% 200776 will-it-scale.per_thread_ops
>>>>>>> brk1/ disable THP 939.67 -6.6% 877.33 will-it-scale.per_thread_ops
>>>>>>> page_fault3/ disable THP 173145 -4.7% 165064 will-it-scale.per_process_ops
>>>>>>> signal1/ disable THP 9162 -3.9% 8802 will-it-scale.per_process_ops
>>>>>>>
>>>>>>> 2. Improvements:
>>>>>>> a) THP enabled:
>>>>>>> testcase base change head metric
>>>>>>> malloc1/ enable THP 66.33 +469.8% 383.67 will-it-scale.per_thread_ops
>>>>>>> writeseek3/ enable THP 2531 +4.5% 2646 will-it-scale.per_thread_ops
>>>>>>> signal1/ enable THP 989.33 +2.8% 1016 will-it-scale.per_thread_ops
>>>>>>>
>>>>>>> b) THP disabled:
>>>>>>> testcase base change head metric
>>>>>>> malloc1/ disable THP 90.33 +417.3% 467.33 will-it-scale.per_thread_ops
>>>>>>> read2/ disable THP 58934 +39.2% 82060 will-it-scale.per_thread_ops
>>>>>>> page_fault1/ disable THP 8607 +36.4% 11736 will-it-scale.per_thread_ops
>>>>>>> read1/ disable THP 314063 +12.7% 353934 will-it-scale.per_thread_ops
>>>>>>> writeseek3/ disable THP 2452 +12.5% 2759 will-it-scale.per_thread_ops
>>>>>>> signal1/ disable THP 971.33 +5.5% 1024 will-it-scale.per_thread_ops
>>>>>>>
>>>>>>> Notes: for above values in column "change", the higher value means that the related testcase result
>>>>>>> on head commit is better than that on base commit for this benchmark.
>>>>>>>
>>>>>>>
>>>>>>> Best regards
>>>>>>> Haiyan Song
>>>>>>>
>>>>>>> ________________________________________
>>>>>>> From: owner-linux-mm@xxxxxxxxx [owner-linux-mm@xxxxxxxxx] on behalf of Laurent Dufour [ldufour@xxxxxxxxxxxxxxxxxx]
>>>>>>> Sent: Thursday, May 17, 2018 7:06 PM
>>>>>>> To: akpm@xxxxxxxxxxxxxxxxxxxx; mhocko@xxxxxxxxxx; peterz@xxxxxxxxxxxxx; kirill@xxxxxxxxxxxxx; ak@xxxxxxxxxxxxxxx; dave@xxxxxxxxxxxx; jack@xxxxxxx; Matthew Wilcox; khandual@xxxxxxxxxxxxxxxxxx; aneesh.kumar@xxxxxxxxxxxxxxxxxx; benh@xxxxxxxxxxxxxxxxxxx; mpe@xxxxxxxxxxxxxx; paulus@xxxxxxxxx; Thomas Gleixner; Ingo Molnar; hpa@xxxxxxxxx; Will Deacon; Sergey Senozhatsky; sergey.senozhatsky.work@xxxxxxxxx; Andrea Arcangeli; Alexei Starovoitov; Wang, Kemi; Daniel Jordan; David Rientjes; Jerome Glisse; Ganesh Mahendran; Minchan Kim; Punit Agrawal; vinayak menon; Yang Shi
>>>>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx; linux-mm@xxxxxxxxx; haren@xxxxxxxxxxxxxxxxxx; npiggin@xxxxxxxxx; bsingharora@xxxxxxxxx; paulmck@xxxxxxxxxxxxxxxxxx; Tim Chen; linuxppc-dev@xxxxxxxxxxxxxxxx; x86@xxxxxxxxxx
>>>>>>> Subject: [PATCH v11 00/26] Speculative page faults
>>>>>>>
>>>>>>> This is a port on kernel 4.17 of the work done by Peter Zijlstra to handle
>>>>>>> page fault without holding the mm semaphore [1].
>>>>>>>
>>>>>>> The idea is to try to handle user space page faults without holding the
>>>>>>> mmap_sem. This should allow better concurrency for massively threaded
>>>>>>> process since the page fault handler will not wait for other threads memory
>>>>>>> layout change to be done, assuming that this change is done in another part
>>>>>>> of the process's memory space. This type page fault is named speculative
>>>>>>> page fault. If the speculative page fault fails because of a concurrency is
>>>>>>> detected or because underlying PMD or PTE tables are not yet allocating, it
>>>>>>> is failing its processing and a classic page fault is then tried.
>>>>>>>
>>>>>>> The speculative page fault (SPF) has to look for the VMA matching the fault
>>>>>>> address without holding the mmap_sem, this is done by introducing a rwlock
>>>>>>> which protects the access to the mm_rb tree. Previously this was done using
>>>>>>> SRCU but it was introducing a lot of scheduling to process the VMA's
>>>>>>> freeing operation which was hitting the performance by 20% as reported by
>>>>>>> Kemi Wang [2]. Using a rwlock to protect access to the mm_rb tree is
>>>>>>> limiting the locking contention to these operations which are expected to
>>>>>>> be in a O(log n) order. In addition to ensure that the VMA is not freed in
>>>>>>> our back a reference count is added and 2 services (get_vma() and
>>>>>>> put_vma()) are introduced to handle the reference count. Once a VMA is
>>>>>>> fetched from the RB tree using get_vma(), it must be later freed using
>>>>>>> put_vma(). I can't see anymore the overhead I got while will-it-scale
>>>>>>> benchmark anymore.
>>>>>>>
>>>>>>> The VMA's attributes checked during the speculative page fault processing
>>>>>>> have to be protected against parallel changes. This is done by using a per
>>>>>>> VMA sequence lock. This sequence lock allows the speculative page fault
>>>>>>> handler to fast check for parallel changes in progress and to abort the
>>>>>>> speculative page fault in that case.
>>>>>>>
>>>>>>> Once the VMA has been found, the speculative page fault handler would check
>>>>>>> for the VMA's attributes to verify that the page fault has to be handled
>>>>>>> correctly or not. Thus, the VMA is protected through a sequence lock which
>>>>>>> allows fast detection of concurrent VMA changes. If such a change is
>>>>>>> detected, the speculative page fault is aborted and a *classic* page fault
>>>>>>> is tried. VMA sequence lockings are added when VMA attributes which are
>>>>>>> checked during the page fault are modified.
>>>>>>>
>>>>>>> When the PTE is fetched, the VMA is checked to see if it has been changed,
>>>>>>> so once the page table is locked, the VMA is valid, so any other changes
>>>>>>> leading to touching this PTE will need to lock the page table, so no
>>>>>>> parallel change is possible at this time.
>>>>>>>
>>>>>>> The locking of the PTE is done with interrupts disabled, this allows
>>>>>>> checking for the PMD to ensure that there is not an ongoing collapsing
>>>>>>> operation. Since khugepaged is firstly set the PMD to pmd_none and then is
>>>>>>> waiting for the other CPU to have caught the IPI interrupt, if the pmd is
>>>>>>> valid at the time the PTE is locked, we have the guarantee that the
>>>>>>> collapsing operation will have to wait on the PTE lock to move forward.
>>>>>>> This allows the SPF handler to map the PTE safely. If the PMD value is
>>>>>>> different from the one recorded at the beginning of the SPF operation, the
>>>>>>> classic page fault handler will be called to handle the operation while
>>>>>>> holding the mmap_sem. As the PTE lock is done with the interrupts disabled,
>>>>>>> the lock is done using spin_trylock() to avoid dead lock when handling a
>>>>>>> page fault while a TLB invalidate is requested by another CPU holding the
>>>>>>> PTE.
>>>>>>>
>>>>>>> In pseudo code, this could be seen as:
>>>>>>> speculative_page_fault()
>>>>>>> {
>>>>>>> vma = get_vma()
>>>>>>> check vma sequence count
>>>>>>> check vma's support
>>>>>>> disable interrupt
>>>>>>> check pgd,p4d,...,pte
>>>>>>> save pmd and pte in vmf
>>>>>>> save vma sequence counter in vmf
>>>>>>> enable interrupt
>>>>>>> check vma sequence count
>>>>>>> handle_pte_fault(vma)
>>>>>>> ..
>>>>>>> page = alloc_page()
>>>>>>> pte_map_lock()
>>>>>>> disable interrupt
>>>>>>> abort if sequence counter has changed
>>>>>>> abort if pmd or pte has changed
>>>>>>> pte map and lock
>>>>>>> enable interrupt
>>>>>>> if abort
>>>>>>> free page
>>>>>>> abort
>>>>>>> ...
>>>>>>> }
>>>>>>>
>>>>>>> arch_fault_handler()
>>>>>>> {
>>>>>>> if (speculative_page_fault(&vma))
>>>>>>> goto done
>>>>>>> again:
>>>>>>> lock(mmap_sem)
>>>>>>> vma = find_vma();
>>>>>>> handle_pte_fault(vma);
>>>>>>> if retry
>>>>>>> unlock(mmap_sem)
>>>>>>> goto again;
>>>>>>> done:
>>>>>>> handle fault error
>>>>>>> }
>>>>>>>
>>>>>>> Support for THP is not done because when checking for the PMD, we can be
>>>>>>> confused by an in progress collapsing operation done by khugepaged. The
>>>>>>> issue is that pmd_none() could be true either if the PMD is not already
>>>>>>> populated or if the underlying PTE are in the way to be collapsed. So we
>>>>>>> cannot safely allocate a PMD if pmd_none() is true.
>>>>>>>
>>>>>>> This series add a new software performance event named 'speculative-faults'
>>>>>>> or 'spf'. It counts the number of successful page fault event handled
>>>>>>> speculatively. When recording 'faults,spf' events, the faults one is
>>>>>>> counting the total number of page fault events while 'spf' is only counting
>>>>>>> the part of the faults processed speculatively.
>>>>>>>
>>>>>>> There are some trace events introduced by this series. They allow
>>>>>>> identifying why the page faults were not processed speculatively. This
>>>>>>> doesn't take in account the faults generated by a monothreaded process
>>>>>>> which directly processed while holding the mmap_sem. This trace events are
>>>>>>> grouped in a system named 'pagefault', they are:
>>>>>>> - pagefault:spf_vma_changed : if the VMA has been changed in our back
>>>>>>> - pagefault:spf_vma_noanon : the vma->anon_vma field was not yet set.
>>>>>>> - pagefault:spf_vma_notsup : the VMA's type is not supported
>>>>>>> - pagefault:spf_vma_access : the VMA's access right are not respected
>>>>>>> - pagefault:spf_pmd_changed : the upper PMD pointer has changed in our
>>>>>>> back.
>>>>>>>
>>>>>>> To record all the related events, the easier is to run perf with the
>>>>>>> following arguments :
>>>>>>> $ perf stat -e 'faults,spf,pagefault:*' <command>
>>>>>>>
>>>>>>> There is also a dedicated vmstat counter showing the number of successful
>>>>>>> page fault handled speculatively. I can be seen this way:
>>>>>>> $ grep speculative_pgfault /proc/vmstat
>>>>>>>
>>>>>>> This series builds on top of v4.16-mmotm-2018-04-13-17-28 and is functional
>>>>>>> on x86, PowerPC and arm64.
>>>>>>>
>>>>>>> ---------------------
>>>>>>> Real Workload results
>>>>>>>
>>>>>>> As mentioned in previous email, we did non official runs using a "popular
>>>>>>> in memory multithreaded database product" on 176 cores SMT8 Power system
>>>>>>> which showed a 30% improvements in the number of transaction processed per
>>>>>>> second. This run has been done on the v6 series, but changes introduced in
>>>>>>> this new version should not impact the performance boost seen.
>>>>>>>
>>>>>>> Here are the perf data captured during 2 of these runs on top of the v8
>>>>>>> series:
>>>>>>> vanilla spf
>>>>>>> faults 89.418 101.364 +13%
>>>>>>> spf n/a 97.989
>>>>>>>
>>>>>>> With the SPF kernel, most of the page fault were processed in a speculative
>>>>>>> way.
>>>>>>>
>>>>>>> Ganesh Mahendran had backported the series on top of a 4.9 kernel and gave
>>>>>>> it a try on an android device. He reported that the application launch time
>>>>>>> was improved in average by 6%, and for large applications (~100 threads) by
>>>>>>> 20%.
>>>>>>>
>>>>>>> Here are the launch time Ganesh mesured on Android 8.0 on top of a Qcom
>>>>>>> MSM845 (8 cores) with 6GB (the less is better):
>>>>>>>
>>>>>>> Application 4.9 4.9+spf delta
>>>>>>> com.tencent.mm 416 389 -7%
>>>>>>> com.eg.android.AlipayGphone 1135 986 -13%
>>>>>>> com.tencent.mtt 455 454 0%
>>>>>>> com.qqgame.hlddz 1497 1409 -6%
>>>>>>> com.autonavi.minimap 711 701 -1%
>>>>>>> com.tencent.tmgp.sgame 788 748 -5%
>>>>>>> com.immomo.momo 501 487 -3%
>>>>>>> com.tencent.peng 2145 2112 -2%
>>>>>>> com.smile.gifmaker 491 461 -6%
>>>>>>> com.baidu.BaiduMap 479 366 -23%
>>>>>>> com.taobao.taobao 1341 1198 -11%
>>>>>>> com.baidu.searchbox 333 314 -6%
>>>>>>> com.tencent.mobileqq 394 384 -3%
>>>>>>> com.sina.weibo 907 906 0%
>>>>>>> com.youku.phone 816 731 -11%
>>>>>>> com.happyelements.AndroidAnimal.qq 763 717 -6%
>>>>>>> com.UCMobile 415 411 -1%
>>>>>>> com.tencent.tmgp.ak 1464 1431 -2%
>>>>>>> com.tencent.qqmusic 336 329 -2%
>>>>>>> com.sankuai.meituan 1661 1302 -22%
>>>>>>> com.netease.cloudmusic 1193 1200 1%
>>>>>>> air.tv.douyu.android 4257 4152 -2%
>>>>>>>
>>>>>>> ------------------
>>>>>>> Benchmarks results
>>>>>>>
>>>>>>> Base kernel is v4.17.0-rc4-mm1
>>>>>>> SPF is BASE + this series
>>>>>>>
>>>>>>> Kernbench:
>>>>>>> ----------
>>>>>>> Here are the results on a 16 CPUs X86 guest using kernbench on a 4.15
>>>>>>> kernel (kernel is build 5 times):
>>>>>>>
>>>>>>> Average Half load -j 8
>>>>>>> Run (std deviation)
>>>>>>> BASE SPF
>>>>>>> Elapsed Time 1448.65 (5.72312) 1455.84 (4.84951) 0.50%
>>>>>>> User Time 10135.4 (30.3699) 10148.8 (31.1252) 0.13%
>>>>>>> System Time 900.47 (2.81131) 923.28 (7.52779) 2.53%
>>>>>>> Percent CPU 761.4 (1.14018) 760.2 (0.447214) -0.16%
>>>>>>> Context Switches 85380 (3419.52) 84748 (1904.44) -0.74%
>>>>>>> Sleeps 105064 (1240.96) 105074 (337.612) 0.01%
>>>>>>>
>>>>>>> Average Optimal load -j 16
>>>>>>> Run (std deviation)
>>>>>>> BASE SPF
>>>>>>> Elapsed Time 920.528 (10.1212) 927.404 (8.91789) 0.75%
>>>>>>> User Time 11064.8 (981.142) 11085 (990.897) 0.18%
>>>>>>> System Time 979.904 (84.0615) 1001.14 (82.5523) 2.17%
>>>>>>> Percent CPU 1089.5 (345.894) 1086.1 (343.545) -0.31%
>>>>>>> Context Switches 159488 (78156.4) 158223 (77472.1) -0.79%
>>>>>>> Sleeps 110566 (5877.49) 110388 (5617.75) -0.16%
>>>>>>>
>>>>>>>
>>>>>>> During a run on the SPF, perf events were captured:
>>>>>>> Performance counter stats for '../kernbench -M':
>>>>>>> 526743764 faults
>>>>>>> 210 spf
>>>>>>> 3 pagefault:spf_vma_changed
>>>>>>> 0 pagefault:spf_vma_noanon
>>>>>>> 2278 pagefault:spf_vma_notsup
>>>>>>> 0 pagefault:spf_vma_access
>>>>>>> 0 pagefault:spf_pmd_changed
>>>>>>>
>>>>>>> Very few speculative page faults were recorded as most of the processes
>>>>>>> involved are monothreaded (sounds that on this architecture some threads
>>>>>>> were created during the kernel build processing).
>>>>>>>
>>>>>>> Here are the kerbench results on a 80 CPUs Power8 system:
>>>>>>>
>>>>>>> Average Half load -j 40
>>>>>>> Run (std deviation)
>>>>>>> BASE SPF
>>>>>>> Elapsed Time 117.152 (0.774642) 117.166 (0.476057) 0.01%
>>>>>>> User Time 4478.52 (24.7688) 4479.76 (9.08555) 0.03%
>>>>>>> System Time 131.104 (0.720056) 134.04 (0.708414) 2.24%
>>>>>>> Percent CPU 3934 (19.7104) 3937.2 (19.0184) 0.08%
>>>>>>> Context Switches 92125.4 (576.787) 92581.6 (198.622) 0.50%
>>>>>>> Sleeps 317923 (652.499) 318469 (1255.59) 0.17%
>>>>>>>
>>>>>>> Average Optimal load -j 80
>>>>>>> Run (std deviation)
>>>>>>> BASE SPF
>>>>>>> Elapsed Time 107.73 (0.632416) 107.31 (0.584936) -0.39%
>>>>>>> User Time 5869.86 (1466.72) 5871.71 (1467.27) 0.03%
>>>>>>> System Time 153.728 (23.8573) 157.153 (24.3704) 2.23%
>>>>>>> Percent CPU 5418.6 (1565.17) 5436.7 (1580.91) 0.33%
>>>>>>> Context Switches 223861 (138865) 225032 (139632) 0.52%
>>>>>>> Sleeps 330529 (13495.1) 332001 (14746.2) 0.45%
>>>>>>>
>>>>>>> During a run on the SPF, perf events were captured:
>>>>>>> Performance counter stats for '../kernbench -M':
>>>>>>> 116730856 faults
>>>>>>> 0 spf
>>>>>>> 3 pagefault:spf_vma_changed
>>>>>>> 0 pagefault:spf_vma_noanon
>>>>>>> 476 pagefault:spf_vma_notsup
>>>>>>> 0 pagefault:spf_vma_access
>>>>>>> 0 pagefault:spf_pmd_changed
>>>>>>>
>>>>>>> Most of the processes involved are monothreaded so SPF is not activated but
>>>>>>> there is no impact on the performance.
>>>>>>>
>>>>>>> Ebizzy:
>>>>>>> -------
>>>>>>> The test is counting the number of records per second it can manage, the
>>>>>>> higher is the best. I run it like this 'ebizzy -mTt <nrcpus>'. To get
>>>>>>> consistent result I repeated the test 100 times and measure the average
>>>>>>> result. The number is the record processes per second, the higher is the
>>>>>>> best.
>>>>>>>
>>>>>>> BASE SPF delta
>>>>>>> 16 CPUs x86 VM 742.57 1490.24 100.69%
>>>>>>> 80 CPUs P8 node 13105.4 24174.23 84.46%
>>>>>>>
>>>>>>> Here are the performance counter read during a run on a 16 CPUs x86 VM:
>>>>>>> Performance counter stats for './ebizzy -mTt 16':
>>>>>>> 1706379 faults
>>>>>>> 1674599 spf
>>>>>>> 30588 pagefault:spf_vma_changed
>>>>>>> 0 pagefault:spf_vma_noanon
>>>>>>> 363 pagefault:spf_vma_notsup
>>>>>>> 0 pagefault:spf_vma_access
>>>>>>> 0 pagefault:spf_pmd_changed
>>>>>>>
>>>>>>> And the ones captured during a run on a 80 CPUs Power node:
>>>>>>> Performance counter stats for './ebizzy -mTt 80':
>>>>>>> 1874773 faults
>>>>>>> 1461153 spf
>>>>>>> 413293 pagefault:spf_vma_changed
>>>>>>> 0 pagefault:spf_vma_noanon
>>>>>>> 200 pagefault:spf_vma_notsup
>>>>>>> 0 pagefault:spf_vma_access
>>>>>>> 0 pagefault:spf_pmd_changed
>>>>>>>
>>>>>>> In ebizzy's case most of the page fault were handled in a speculative way,
>>>>>>> leading the ebizzy performance boost.
>>>>>>>
>>>>>>> ------------------
>>>>>>> Changes since v10 (https://lkml.org/lkml/2018/4/17/572):
>>>>>>> - Accounted for all review feedbacks from Punit Agrawal, Ganesh Mahendran
>>>>>>> and Minchan Kim, hopefully.
>>>>>>> - Remove unneeded check on CONFIG_SPECULATIVE_PAGE_FAULT in
>>>>>>> __do_page_fault().
>>>>>>> - Loop in pte_spinlock() and pte_map_lock() when pte try lock fails
>>>>>>> instead
>>>>>>> of aborting the speculative page fault handling. Dropping the now
>>>>>>> useless
>>>>>>> trace event pagefault:spf_pte_lock.
>>>>>>> - No more try to reuse the fetched VMA during the speculative page fault
>>>>>>> handling when retrying is needed. This adds a lot of complexity and
>>>>>>> additional tests done didn't show a significant performance improvement.
>>>>>>> - Convert IS_ENABLED(CONFIG_NUMA) back to #ifdef due to build error.
>>>>>>>
>>>>>>> [1] http://linux-kernel.2935.n7.nabble.com/RFC-PATCH-0-6-Another-go-at-speculative-page-faults-tt965642.html#none
>>>>>>> [2] https://patchwork.kernel.org/patch/9999687/
>>>>>>>
>>>>>>>
>>>>>>> Laurent Dufour (20):
>>>>>>> mm: introduce CONFIG_SPECULATIVE_PAGE_FAULT
>>>>>>> x86/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>>>> powerpc/mm: set ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>>>> mm: introduce pte_spinlock for FAULT_FLAG_SPECULATIVE
>>>>>>> mm: make pte_unmap_same compatible with SPF
>>>>>>> mm: introduce INIT_VMA()
>>>>>>> mm: protect VMA modifications using VMA sequence count
>>>>>>> mm: protect mremap() against SPF hanlder
>>>>>>> mm: protect SPF handler against anon_vma changes
>>>>>>> mm: cache some VMA fields in the vm_fault structure
>>>>>>> mm/migrate: Pass vm_fault pointer to migrate_misplaced_page()
>>>>>>> mm: introduce __lru_cache_add_active_or_unevictable
>>>>>>> mm: introduce __vm_normal_page()
>>>>>>> mm: introduce __page_add_new_anon_rmap()
>>>>>>> mm: protect mm_rb tree with a rwlock
>>>>>>> mm: adding speculative page fault failure trace events
>>>>>>> perf: add a speculative page fault sw event
>>>>>>> perf tools: add support for the SPF perf event
>>>>>>> mm: add speculative page fault vmstats
>>>>>>> powerpc/mm: add speculative page fault
>>>>>>>
>>>>>>> Mahendran Ganesh (2):
>>>>>>> arm64/mm: define ARCH_SUPPORTS_SPECULATIVE_PAGE_FAULT
>>>>>>> arm64/mm: add speculative page fault
>>>>>>>
>>>>>>> Peter Zijlstra (4):
>>>>>>> mm: prepare for FAULT_FLAG_SPECULATIVE
>>>>>>> mm: VMA sequence count
>>>>>>> mm: provide speculative fault infrastructure
>>>>>>> x86/mm: add speculative pagefault handling
>>>>>>>
>>>>>>> arch/arm64/Kconfig | 1 +
>>>>>>> arch/arm64/mm/fault.c | 12 +
>>>>>>> arch/powerpc/Kconfig | 1 +
>>>>>>> arch/powerpc/mm/fault.c | 16 +
>>>>>>> arch/x86/Kconfig | 1 +
>>>>>>> arch/x86/mm/fault.c | 27 +-
>>>>>>> fs/exec.c | 2 +-
>>>>>>> fs/proc/task_mmu.c | 5 +-
>>>>>>> fs/userfaultfd.c | 17 +-
>>>>>>> include/linux/hugetlb_inline.h | 2 +-
>>>>>>> include/linux/migrate.h | 4 +-
>>>>>>> include/linux/mm.h | 136 +++++++-
>>>>>>> include/linux/mm_types.h | 7 +
>>>>>>> include/linux/pagemap.h | 4 +-
>>>>>>> include/linux/rmap.h | 12 +-
>>>>>>> include/linux/swap.h | 10 +-
>>>>>>> include/linux/vm_event_item.h | 3 +
>>>>>>> include/trace/events/pagefault.h | 80 +++++
>>>>>>> include/uapi/linux/perf_event.h | 1 +
>>>>>>> kernel/fork.c | 5 +-
>>>>>>> mm/Kconfig | 22 ++
>>>>>>> mm/huge_memory.c | 6 +-
>>>>>>> mm/hugetlb.c | 2 +
>>>>>>> mm/init-mm.c | 3 +
>>>>>>> mm/internal.h | 20 ++
>>>>>>> mm/khugepaged.c | 5 +
>>>>>>> mm/madvise.c | 6 +-
>>>>>>> mm/memory.c | 612 +++++++++++++++++++++++++++++-----
>>>>>>> mm/mempolicy.c | 51 ++-
>>>>>>> mm/migrate.c | 6 +-
>>>>>>> mm/mlock.c | 13 +-
>>>>>>> mm/mmap.c | 229 ++++++++++---
>>>>>>> mm/mprotect.c | 4 +-
>>>>>>> mm/mremap.c | 13 +
>>>>>>> mm/nommu.c | 2 +-
>>>>>>> mm/rmap.c | 5 +-
>>>>>>> mm/swap.c | 6 +-
>>>>>>> mm/swap_state.c | 8 +-
>>>>>>> mm/vmstat.c | 5 +-
>>>>>>> tools/include/uapi/linux/perf_event.h | 1 +
>>>>>>> tools/perf/util/evsel.c | 1 +
>>>>>>> tools/perf/util/parse-events.c | 4 +
>>>>>>> tools/perf/util/parse-events.l | 1 +
>>>>>>> tools/perf/util/python.c | 1 +
>>>>>>> 44 files changed, 1161 insertions(+), 211 deletions(-)
>>>>>>> create mode 100644 include/trace/events/pagefault.h
>>>>>>>
>>>>>>> --
>>>>>>> 2.7.4
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>>
>>
>
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