From: Chao Fan <cfan@xxxxxxxxxx>
Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
Date: Wed, 23 Dec 2015 22:31:37 -0500
>
>
> ----- Original Message -----
>> From: "HATAYAMA Daisuke" <d.hatayama at jp.fujitsu.com>
>> To: cfan at redhat.com
>> Cc: ats-kumagai at wm.jp.nec.com, zhouwj-fnst at cn.fujitsu.com, kexec at lists.infradead.org
>> Sent: Thursday, December 24, 2015 11:22:28 AM
>> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>>
>> From: Chao Fan <cfan at redhat.com>
>> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>> Date: Wed, 23 Dec 2015 21:20:48 -0500
>>
>> >
>> >
>> > ----- Original Message -----
>> >> From: "HATAYAMA Daisuke" <d.hatayama at jp.fujitsu.com>
>> >> To: cfan at redhat.com
>> >> Cc: ats-kumagai at wm.jp.nec.com, zhouwj-fnst at cn.fujitsu.com,
>> >> kexec at lists.infradead.org
>> >> Sent: Tuesday, December 22, 2015 4:32:25 PM
>> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>> >>
>> >> Chao,
>> >>
>> >> From: Chao Fan <cfan at redhat.com>
>> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>> >> Date: Thu, 10 Dec 2015 05:54:28 -0500
>> >>
>> >> >
>> >> >
>> >> > ----- Original Message -----
>> >> >> From: "Wenjian Zhou/???" <zhouwj-fnst at cn.fujitsu.com>
>> >> >> To: "Chao Fan" <cfan at redhat.com>
>> >> >> Cc: "Atsushi Kumagai" <ats-kumagai at wm.jp.nec.com>,
>> >> >> kexec at lists.infradead.org
>> >> >> Sent: Thursday, December 10, 2015 6:32:32 PM
>> >> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>> >> >>
>> >> >> On 12/10/2015 05:58 PM, Chao Fan wrote:
>> >> >> >
>> >> >> >
>> >> >> > ----- Original Message -----
>> >> >> >> From: "Wenjian Zhou/???" <zhouwj-fnst at cn.fujitsu.com>
>> >> >> >> To: "Atsushi Kumagai" <ats-kumagai at wm.jp.nec.com>
>> >> >> >> Cc: kexec at lists.infradead.org
>> >> >> >> Sent: Thursday, December 10, 2015 5:36:47 PM
>> >> >> >> Subject: Re: [PATCH RFC 00/11] makedumpfile: parallel processing
>> >> >> >>
>> >> >> >> On 12/10/2015 04:14 PM, Atsushi Kumagai wrote:
>> >> >> >>>> Hello Kumagai,
>> >> >> >>>>
>> >> >> >>>> On 12/04/2015 10:30 AM, Atsushi Kumagai wrote:
>> >> >> >>>>> Hello, Zhou
>> >> >> >>>>>
>> >> >> >>>>>> On 12/02/2015 03:24 PM, Dave Young wrote:
>> >> >> >>>>>>> Hi,
>> >> >> >>>>>>>
>> >> >> >>>>>>> On 12/02/15 at 01:29pm, "Zhou, Wenjian/???" wrote:
>> >> >> >>>>>>>> I think there is no problem if other test results are as
>> >> >> >>>>>>>> expected.
>> >> >> >>>>>>>>
>> >> >> >>>>>>>> --num-threads mainly reduces the time of compressing.
>> >> >> >>>>>>>> So for lzo, it can't do much help at most of time.
>> >> >> >>>>>>>
>> >> >> >>>>>>> Seems the help of --num-threads does not say it exactly:
>> >> >> >>>>>>>
>> >> >> >>>>>>> [--num-threads THREADNUM]:
>> >> >> >>>>>>> Using multiple threads to read and compress data of
>> >> >> >>>>>>> each
>> >> >> >>>>>>> page
>> >> >> >>>>>>> in parallel.
>> >> >> >>>>>>> And it will reduces time for saving DUMPFILE.
>> >> >> >>>>>>> This feature only supports creating DUMPFILE in
>> >> >> >>>>>>> kdump-comressed format from
>> >> >> >>>>>>> VMCORE in kdump-compressed format or elf format.
>> >> >> >>>>>>>
>> >> >> >>>>>>> Lzo is also a compress method, it should be mentioned that
>> >> >> >>>>>>> --num-threads only
>> >> >> >>>>>>> supports zlib compressed vmcore.
>> >> >> >>>>>>>
>> >> >> >>>>>>
>> >> >> >>>>>> Sorry, it seems that something I said is not so clear.
>> >> >> >>>>>> lzo is also supported. Since lzo compresses data at a high
>> >> >> >>>>>> speed,
>> >> >> >>>>>> the
>> >> >> >>>>>> improving of the performance is not so obvious at most of time.
>> >> >> >>>>>>
>> >> >> >>>>>>> Also worth to mention about the recommended -d value for this
>> >> >> >>>>>>> feature.
>> >> >> >>>>>>>
>> >> >> >>>>>>
>> >> >> >>>>>> Yes, I think it's worth. I forgot it.
>> >> >> >>>>>
>> >> >> >>>>> I saw your patch, but I think I should confirm what is the
>> >> >> >>>>> problem
>> >> >> >>>>> first.
>> >> >> >>>>>
>> >> >> >>>>>> However, when "-d 31" is specified, it will be worse.
>> >> >> >>>>>> Less than 50 buffers are used to cache the compressed page.
>> >> >> >>>>>> And even the page has been filtered, it will also take a buffer.
>> >> >> >>>>>> So if "-d 31" is specified, the filtered page will use a lot
>> >> >> >>>>>> of buffers. Then the page which needs to be compressed can't
>> >> >> >>>>>> be compressed parallel.
>> >> >> >>>>>
>> >> >> >>>>> Could you explain why compression will not be parallel in more
>> >> >> >>>>> detail ?
>> >> >> >>>>> Actually the buffers are used also for filtered pages, it sounds
>> >> >> >>>>> inefficient.
>> >> >> >>>>> However, I don't understand why it prevents parallel compression.
>> >> >> >>>>>
>> >> >> >>>>
>> >> >> >>>> Think about this, in a huge memory, most of the page will be
>> >> >> >>>> filtered,
>> >> >> >>>> and
>> >> >> >>>> we have 5 buffers.
>> >> >> >>>>
>> >> >> >>>> page1 page2 page3 page4 page5 page6
>> >> >> >>>> page7
>> >> >> >>>> .....
>> >> >> >>>> [buffer1] [2] [3] [4] [5]
>> >> >> >>>> unfiltered filtered filtered filtered filtered unfiltered
>> >> >> >>>> filtered
>> >> >> >>>>
>> >> >> >>>> Since filtered page will take a buffer, when compressing page1,
>> >> >> >>>> page6 can't be compressed at the same time.
>> >> >> >>>> That why it will prevent parallel compression.
>> >> >> >>>
>> >> >> >>> Thanks for your explanation, I understand.
>> >> >> >>> This is just an issue of the current implementation, there is no
>> >> >> >>> reason to stand this restriction.
>> >> >> >>>
>> >> >> >>>>> Further, according to Chao's benchmark, there is a big
>> >> >> >>>>> performance
>> >> >> >>>>> degradation even if the number of thread is 1. (58s vs 240s)
>> >> >> >>>>> The current implementation seems to have some problems, we should
>> >> >> >>>>> solve them.
>> >> >> >>>>>
>> >> >> >>>>
>> >> >> >>>> If "-d 31" is specified, on the one hand we can't save time by
>> >> >> >>>> compressing
>> >> >> >>>> parallel, on the other hand we will introduce some extra work by
>> >> >> >>>> adding
>> >> >> >>>> "--num-threads". So it is obvious that it will have a performance
>> >> >> >>>> degradation.
>> >> >> >>>
>> >> >> >>> Sure, there must be some overhead due to "some extra work"(e.g.
>> >> >> >>> exclusive
>> >> >> >>> lock),
>> >> >> >>> but "--num-threads=1 is 4 times slower than --num-threads=0" still
>> >> >> >>> sounds
>> >> >> >>> too slow, the degradation is too big to be called "some extra
>> >> >> >>> work".
>> >> >> >>>
>> >> >> >>> Both --num-threads=0 and --num-threads=1 are serial processing,
>> >> >> >>> the above "buffer fairness issue" will not be related to this
>> >> >> >>> degradation.
>> >> >> >>> What do you think what make this degradation ?
>> >> >> >>>
>> >> >> >>
>> >> >> >> I can't get such result at this moment, so I can't do some further
>> >> >> >> investigation
>> >> >> >> right now. I guess it may be caused by the underlying implementation
>> >> >> >> of
>> >> >> >> pthread.
>> >> >> >> I reviewed the test result of the patch v2 and found in different
>> >> >> >> machines,
>> >> >> >> the results are quite different.
>> >> >> >
>> >> >> > Hi Zhou Wenjian,
>> >> >> >
>> >> >> > I have done more tests in another machine with 128G memory, and get
>> >> >> > the
>> >> >> > result:
>> >> >> >
>> >> >> > the size of vmcore is 300M in "-d 31"
>> >> >> > makedumpfile -l --message-level 1 -d 31:
>> >> >> > time: 8.6s page-faults: 2272
>> >> >> >
>> >> >> > makedumpfile -l --num-threads 1 --message-level 1 -d 31:
>> >> >> > time: 28.1s page-faults: 2359
>> >> >> >
>> >> >> >
>> >> >> > and the size of vmcore is 2.6G in "-d 0".
>> >> >> > In this machine, I get the same result as yours:
>> >> >> >
>> >> >> >
>> >> >> > makedumpfile -c --message-level 1 -d 0:
>> >> >> > time: 597s page-faults: 2287
>> >> >> >
>> >> >> > makedumpfile -c --num-threads 1 --message-level 1 -d 0:
>> >> >> > time: 602s page-faults: 2361
>> >> >> >
>> >> >> > makedumpfile -c --num-threads 2 --message-level 1 -d 0:
>> >> >> > time: 337s page-faults: 2397
>> >> >> >
>> >> >> > makedumpfile -c --num-threads 4 --message-level 1 -d 0:
>> >> >> > time: 175s page-faults: 2461
>> >> >> >
>> >> >> > makedumpfile -c --num-threads 8 --message-level 1 -d 0:
>> >> >> > time: 103s page-faults: 2611
>> >> >> >
>> >> >> >
>> >> >> > But the machine of my first test is not under my control, should I
>> >> >> > wait
>> >> >> > for
>> >> >> > the first machine to do more tests?
>> >> >> > If there are still some problems in my tests, please tell me.
>> >> >> >
>> >> >>
>> >> >> Thanks a lot for your test, it seems that there is nothing wrong.
>> >> >> And I haven't got any idea about more tests...
>> >> >>
>> >> >> Could you provide the information of your cpu ?
>> >> >> I will do some further investigation later.
>> >> >>
>> >> >
>> >> > OK, of course, here is the information of cpu:
>> >> >
>> >> > # lscpu
>> >> > Architecture: x86_64
>> >> > CPU op-mode(s): 32-bit, 64-bit
>> >> > Byte Order: Little Endian
>> >> > CPU(s): 48
>> >> > On-line CPU(s) list: 0-47
>> >> > Thread(s) per core: 1
>> >> > Core(s) per socket: 6
>> >> > Socket(s): 8
>> >> > NUMA node(s): 8
>> >> > Vendor ID: AuthenticAMD
>> >> > CPU family: 16
>> >> > Model: 8
>> >> > Model name: Six-Core AMD Opteron(tm) Processor 8439 SE
>> >> > Stepping: 0
>> >> > CPU MHz: 2793.040
>> >> > BogoMIPS: 5586.22
>> >> > Virtualization: AMD-V
>> >> > L1d cache: 64K
>> >> > L1i cache: 64K
>> >> > L2 cache: 512K
>> >> > L3 cache: 5118K
>> >> > NUMA node0 CPU(s): 0,8,16,24,32,40
>> >> > NUMA node1 CPU(s): 1,9,17,25,33,41
>> >> > NUMA node2 CPU(s): 2,10,18,26,34,42
>> >> > NUMA node3 CPU(s): 3,11,19,27,35,43
>> >> > NUMA node4 CPU(s): 4,12,20,28,36,44
>> >> > NUMA node5 CPU(s): 5,13,21,29,37,45
>> >> > NUMA node6 CPU(s): 6,14,22,30,38,46
>> >> > NUMA node7 CPU(s): 7,15,23,31,39,47
>> >>
>> >> This CPU assignment on NUMA nodes looks interesting. Is it possible
>> >> that this affects performance of makedumpfile? This is just a guess.
>> >>
>> >> Could you check whether the performance gets imporoved if you run each
>> >> thread on the same NUMA node? For example:
>> >>
>> >> # taskset -c 0,8,16,24 makedumpfile --num-threads 4 -c -d 0 vmcore
>> >> vmcore-cd0
>> >>
>> > Hi HATAYAMA,
>> >
>> > I think your guess is right, but maybe your command has a little problem.
>> >
>> > From my test, the NUMA did affect the performance, but not too much.
>> > The average time of cpus in the same NUMA node:
>> > # taskset -c 0,8,16,24,32 makedumpfile --num-threads 4 -c -d 0 vmcore
>> > vmcore-cd0
>> > is 314s
>> > The average time of cpus in different NUMA node:
>> > # taskset -c 2,3,5,6,7 makedumpfile --num-threads 4 -c -d 0 vmcore
>> > vmcore-cd0
>> > is 354s
>> >
>>
>> Hmm, according to some previous discussion, what we should see here is
>> whether it affects performance of makedumpfile with --num-threads 1
>> and -d 31. So you should need to compare:
>>
>> # taskset 0,8 makedumpfile --num-threads 1 -c -d 31 vmcore vmcore-d31
>>
>> with:
>>
>> # taskset 0 makedumpfile -c -d 0 vmcore vmcore-d31
I removed -c option wrongly. What I wanted to write is:
# taskset -c 0,8 makedumpfile --num-threads 1 -d 31 vmcore vmcore-d31
and:
# taskset -c 0 makedumpfile -d 31 vmcore vmcore-d31
just in case...
>>
>> Also, I'm assuming that you've done these benchmark on kdump 1st
>> kernel, not kdump 2nd kernel. Is this correct?
>>
> Hi HATAYAMA,
>
> I test in the first kernel, not in the kdump second kernel.
>
I see.
--
Thanks.
HATAYAMA, Daisuke
