On Sun, 4 Oct 2020, kernel test robot wrote:
> Greeting,
>
> FYI, we noticed a -8.7% regression of vm-scalability.throughput due to commit:
>
>
> commit: 85b9f46e8ea451633ccd60a7d8cacbfff9f34047 ("mm, thp: track fallbacks
> due to failed memcg charges separately")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
>
>
> in testcase: vm-scalability
> on test machine: 104 threads Skylake with 192G memory
> with following parameters:
>
> runtime: 300s
> size: 1T
> test: lru-shm
> cpufreq_governor: performance
> ucode: 0x2006906
>
> test-description: The motivation behind this suite is to exercise functions
> and regions of the mm/ of the Linux kernel which are of interest to us.
> test-url: https://git.kernel.org/cgit/linux/kernel/git/wfg/vm-scalability.git/
>
>
>
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <rong.a.c...@intel.com>
>
>
> Details are as below:
> -------------------------------------------------------------------------------------------------->
>
>
> To reproduce:
>
> git clone https://github.com/intel/lkp-tests.git
> cd lkp-tests
> bin/lkp install job.yaml # job file is attached in this email
> bin/lkp run job.yaml
>
> =========================================================================================
> compiler/cpufreq_governor/kconfig/rootfs/runtime/size/tbox_group/test/testcase/ucode:
>
> gcc-9/performance/x86_64-rhel-8.3/debian-10.4-x86_64-20200603.cgz/300s/1T/lkp-skl-fpga01/lru-shm/vm-scalability/0x2006906
>
> commit:
> dcdf11ee14 ("mm, shmem: add vmstat for hugepage fallback")
> 85b9f46e8e ("mm, thp: track fallbacks due to failed memcg charges
> separately")
>
> dcdf11ee14413332 85b9f46e8ea451633ccd60a7d8c
> ---------------- ---------------------------
> fail:runs %reproduction fail:runs
> | | |
> 1:4 24% 2:4
> perf-profile.calltrace.cycles-pp.sync_regs.error_entry.do_access
> 3:4 53% 5:4
> perf-profile.calltrace.cycles-pp.error_entry.do_access
> 9:4 -27% 8:4
> perf-profile.children.cycles-pp.error_entry
> 4:4 -10% 4:4
> perf-profile.self.cycles-pp.error_entry
> %stddev %change %stddev
> \ | \
> 477291 -9.1% 434041 vm-scalability.median
> 49791027 -8.7% 45476799 vm-scalability.throughput
> 223.67 +1.6% 227.36 vm-scalability.time.elapsed_time
> 223.67 +1.6% 227.36
> vm-scalability.time.elapsed_time.max
> 50364 ± 6% +24.1% 62482 ± 10%
> vm-scalability.time.involuntary_context_switches
> 2237 +7.8% 2412
> vm-scalability.time.percent_of_cpu_this_job_got
> 3084 +18.2% 3646 vm-scalability.time.system_time
> 1921 -4.2% 1839 vm-scalability.time.user_time
> 13.68 +2.2 15.86 mpstat.cpu.all.sys%
> 28535 ± 30% -47.0% 15114 ± 79% numa-numastat.node0.other_node
> 142734 ± 11% -19.4% 115000 ± 17% numa-meminfo.node0.AnonPages
> 11168 ± 3% +8.8% 12150 ± 5% numa-meminfo.node1.PageTables
> 76.00 -1.6% 74.75 vmstat.cpu.id
> 3626 -1.9% 3555 vmstat.system.cs
> 2214928 ±166% -96.6% 75321 ± 7% cpuidle.C1.usage
> 200981 ± 7% -18.0% 164861 ± 7% cpuidle.POLL.time
> 52675 ± 3% -16.7% 43866 ± 10% cpuidle.POLL.usage
> 35659 ± 11% -19.4% 28754 ± 17% numa-vmstat.node0.nr_anon_pages
> 1248014 ± 3% +10.9% 1384236 numa-vmstat.node1.nr_mapped
> 2722 ± 4% +10.6% 3011 ± 5%
> numa-vmstat.node1.nr_page_table_pages
I'm not sure that I'm reading this correctly, but I suspect that this just
happens because of NUMA: memory affinity will obviously impact
vm-scalability.throughput quite substantially, but I don't think the
bisected commit can be to be blame. Commit 85b9f46e8ea4 ("mm, thp: track
fallbacks due to failed memcg charges separately") simply adds new
count_vm_event() calls in a couple areas to track thp fallback due to
memcg limits separate from fragmentation.
It's likely a question about the testing methodology in general: for
memory intensive benchmarks, I suggest it is configured in a manner that
we can expect consistent memory access latency at the hardware level when
running on a NUMA system.
