Quick run with hackbench and unixbench on large intel, amd, and arm machines
Patch was applied to 6.1.38
hackbench
Intel performance -2.9% - +1.57% SReclaim -3.2% SUnreclaim -2.4%
Amd performance -28% - +7.58% SReclaim +21.31 SUnreclaim +20.72
ARM performance -0.6 - +1.6% SReclaim +24% SUnreclaim +70%
unixbench
Intel performance -1.4 - +1.59% SReclaimm -1.65% SUnreclaim -1.59%
Amd performance -1.9% - +1.05% SReclaim -3.1% SUnreclaimm -0.81%
ARM performance -0.09% - +0.54% SReclaimm -1.05% SUnreclaim -2.03%
AMD Hackbench
28% drop on hackbench_thread_pipes_234
On Thu, Jul 20, 2023 at 11:08 AM Hyeonggon Yoo <42.hyeyoo@xxxxxxxxx> wrote:
>
> On Thu, Jul 20, 2023 at 11:16 PM Feng Tang <feng.tang@xxxxxxxxx> wrote:
> >
> > Hi Hyeonggon,
> >
> > On Thu, Jul 20, 2023 at 08:59:56PM +0800, Hyeonggon Yoo wrote:
> > > On Thu, Jul 20, 2023 at 12:01 PM Oliver Sang <oliver.sang@xxxxxxxxx> wrote:
> > > >
> > > > hi, Hyeonggon Yoo,
> > > >
> > > > On Tue, Jul 18, 2023 at 03:43:16PM +0900, Hyeonggon Yoo wrote:
> > > > > On Mon, Jul 17, 2023 at 10:41 PM kernel test robot
> > > > > <oliver.sang@xxxxxxxxx> wrote:
> > > > > >
> > > > > >
> > > > > >
> > > > > > Hello,
> > > > > >
> > > > > > kernel test robot noticed a -12.5% regression of hackbench.throughput on:
> > > > > >
> > > > > >
> > > > > > commit: a0fd217e6d6fbd23e91f8796787b621e7d576088 ("[PATCH] [RFC PATCH v2]mm/slub: Optimize slub memory usage")
> > > > > > url: https://github.com/intel-lab-lkp/linux/commits/Jay-Patel/mm-slub-Optimize-slub-memory-usage/20230628-180050
> > > > > > base: git://git.kernel.org/cgit/linux/kernel/git/vbabka/slab.git for-next
> > > > > > patch link: https://lore.kernel.org/all/20230628095740.589893-1-jaypatel@xxxxxxxxxxxxx/
> > > > > > patch subject: [PATCH] [RFC PATCH v2]mm/slub: Optimize slub memory usage
> > > > > >
> > > > > > testcase: hackbench
> > > > > > test machine: 128 threads 2 sockets Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz (Ice Lake) with 256G memory
> > > > > > parameters:
> > > > > >
> > > > > > nr_threads: 100%
> > > > > > iterations: 4
> > > > > > mode: process
> > > > > > ipc: socket
> > > > > > cpufreq_governor: performance
> > > > > >
> > > > > >
> > > > > >
> > > > > >
> > > > > > If you fix the issue in a separate patch/commit (i.e. not just a new version of
> > > > > > the same patch/commit), kindly add following tags
> > > > > > | Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> > > > > > | Closes: https://lore.kernel.org/oe-lkp/202307172140.3b34825a-oliver.sang@xxxxxxxxx
> > > > > >
> > > > > >
> > > > > > Details are as below:
> > > > > > -------------------------------------------------------------------------------------------------->
> > > > > >
> > > > > >
> > > > > > To reproduce:
> > > > > >
> > > > > > git clone https://github.com/intel/lkp-tests.git
> > > > > > cd lkp-tests
> > > > > > sudo bin/lkp install job.yaml # job file is attached in this email
> > > > > > bin/lkp split-job --compatible job.yaml # generate the yaml file for lkp run
> > > > > > sudo bin/lkp run generated-yaml-file
> > > > > >
> > > > > > # if come across any failure that blocks the test,
> > > > > > # please remove ~/.lkp and /lkp dir to run from a clean state.
> > > > > >
> > > > > > =========================================================================================
> > > > > > compiler/cpufreq_governor/ipc/iterations/kconfig/mode/nr_threads/rootfs/tbox_group/testcase:
> > > > > > gcc-12/performance/socket/4/x86_64-rhel-8.3/process/100%/debian-11.1-x86_64-20220510.cgz/lkp-icl-2sp2/hackbench
> > > > > >
> > > > > > commit:
> > > > > > 7bc162d5cc ("Merge branches 'slab/for-6.5/prandom', 'slab/for-6.5/slab_no_merge' and 'slab/for-6.5/slab-deprecate' into slab/for-next")
> > > > > > a0fd217e6d ("mm/slub: Optimize slub memory usage")
> > > > > >
> > > > > > 7bc162d5cc4de5c3 a0fd217e6d6fbd23e91f8796787
> > > > > > ---------------- ---------------------------
> > > > > > %stddev %change %stddev
> > > > > > \ | \
> > > > > > 222503 ą 86% +108.7% 464342 ą 58% numa-meminfo.node1.Active
> > > > > > 222459 ą 86% +108.7% 464294 ą 58% numa-meminfo.node1.Active(anon)
> > > > > > 55573 ą 85% +108.0% 115619 ą 58% numa-vmstat.node1.nr_active_anon
> > > > > > 55573 ą 85% +108.0% 115618 ą 58% numa-vmstat.node1.nr_zone_active_anon
> > > > >
> > > > > I'm quite baffled while reading this.
> > > > > How did changing slab order calculation double the number of active anon pages?
> > > > > I doubt two experiments were performed on the same settings.
> > > >
> > > > let me introduce our test process.
> > > >
> > > > we make sure the tests upon commit and its parent have exact same environment
> > > > except the kernel difference, and we also make sure the config to build the
> > > > commit and its parent are identical.
> > > >
> > > > we run tests for one commit at least 6 times to make sure the data is stable.
> > > >
> > > > such like for this case, we rebuild the commit and its parent's kernel, the
> > > > config is attached FYI.
> > >
> > > Hello Oliver,
> > >
> > > Thank you for confirming the testing environment is totally fine.
> > > and I'm sorry. I didn't mean to offend that your tests were bad.
> > >
> > > It was more like "oh, the data totally doesn't make sense to me"
> > > and I blamed the tests rather than my poor understanding of the data ;)
> > >
> > > Anyway,
> > > as the data shows a repeatable regression,
> > > let's think more about the possible scenario:
> > >
> > > I can't stop thinking that the patch must've affected the system's
> > > reclamation behavior in some way.
> > > (I think more active anon pages with a similar number total of anon
> > > pages implies the kernel scanned more pages)
> > >
> > > It might be because kswapd was more frequently woken up (possible if
> > > skbs were allocated with GFP_ATOMIC)
> > > But the data provided is not enough to support this argument.
> > >
> > > > 2.43 ± 7% +4.5 6.90 ± 11% perf-profile.children.cycles-pp.get_partial_node
> > > > 3.23 ± 5% +4.5 7.77 ± 9% perf-profile.children.cycles-pp.___slab_alloc
> > > > 7.51 ± 2% +4.6 12.11 ± 5% perf-profile.children.cycles-pp.kmalloc_reserve
> > > > 6.94 ± 2% +4.7 11.62 ± 6% perf-profile.children.cycles-pp.__kmalloc_node_track_caller
> > > > 6.46 ± 2% +4.8 11.22 ± 6% perf-profile.children.cycles-pp.__kmem_cache_alloc_node
> > > > 8.48 ± 4% +7.9 16.42 ± 8% perf-profile.children.cycles-pp._raw_spin_lock_irqsave
> > > > 6.12 ± 6% +8.6 14.74 ± 9% perf-profile.children.cycles-pp.native_queued_spin_lock_slowpath
> > >
> > > And this increased cycles in the SLUB slowpath implies that the actual
> > > number of objects available in
> > > the per cpu partial list has been decreased, possibly because of
> > > inaccuracy in the heuristic?
> > > (cuz the assumption that slabs cached per are half-filled, and that
> > > slabs' order is s->oo)
> >
> > From the patch:
> >
> > static unsigned int slub_max_order =
> > - IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : PAGE_ALLOC_COSTLY_ORDER;
> > + IS_ENABLED(CONFIG_SLUB_TINY) ? 1 : 2;
> >
> > Could this be related? that it reduces the order for some slab cache,
> > so each per-cpu slab will has less objects, which makes the contention
> > for per-node spinlock 'list_lock' more severe when the slab allocation
> > is under pressure from many concurrent threads.
>
> hackbench uses skbuff_head_cache intensively. So we need to check if
> skbuff_head_cache's
> order was increased or decreased. On my desktop skbuff_head_cache's
> order is 1 and I roughly
> guessed it was increased, (but it's still worth checking in the testing env)
>
> But decreased slab order does not necessarily mean decreased number
> of cached objects per CPU, because when oo_order(s->oo) is smaller,
> then it caches
> more slabs into the per cpu slab list.
>
> I think more problematic situation is when oo_order(s->oo) is higher,
> because the heuristic
> in SLUB assumes that each slab has order of oo_order(s->oo) and it's
> half-filled. if it allocates
> slabs with order lower than oo_order(s->oo), the number of cached
> objects per CPU
> decreases drastically due to the inaccurate assumption.
>
> So yeah, decreased number of cached objects per CPU could be the cause
> of the regression due to the heuristic.
>
> And I have another theory: it allocated high order slabs from remote node
> even if there are slabs with lower order in the local node.
>
> ofc we need further experiment, but I think both improving the
> accuracy of heuristic and
> avoiding allocating high order slabs from remote nodes would make SLUB
> more robust.
>
> > I don't have direct data to backup it, and I can try some experiment.
>
> Thank you for taking time for experiment!
>
> Thanks,
> Hyeonggon
>
> > > > then retest on this test machine:
> > > > 128 threads 2 sockets Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz (Ice Lake) with 256G memory
>
