Re: [linus:master] [mm] f1a7941243: unixbench.score -19.2% regression

[Matthew Wilcox <willy@infradead.org>]

On Mon, Jan 30, 2023 at 10:32:56AM +0800, kernel test robot wrote:
> FYI, we noticed a -19.2% regression of unixbench.score due to commit:
> 
> commit: f1a7941243c102a44e8847e3b94ff4ff3ec56f25 ("mm: convert mm's rss stats into percpu_counter")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: unixbench
> on test machine: 128 threads 4 sockets Intel(R) Xeon(R) Gold 6338 CPU @ 2.00GHz (Ice Lake) with 256G memory
> with following parameters:
> 
> 	runtime: 300s
> 	nr_task: 30%
> 	test: spawn
> 	cpufreq_governor: performance

...

> 9cd6ffa60256e931 f1a7941243c102a44e8847e3b94 
> ---------------- --------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>      11110           -19.2%       8974        unixbench.score
>    1090843           -12.2%     957314        unixbench.time.involuntary_context_switches
>    4243909 ±  6%     -32.4%    2867136 ±  5%  unixbench.time.major_page_faults
>      10547           -12.6%       9216        unixbench.time.maximum_resident_set_size
>  9.913e+08           -19.6%  7.969e+08        unixbench.time.minor_page_faults
>       5638           +19.1%       6714        unixbench.time.system_time
>       5502           -20.7%       4363        unixbench.time.user_time

So we're spending a lot more time in the kernel and correspondingly less
time in userspace.

>   67991885           -16.9%   56507507        unixbench.time.voluntary_context_switches
>   46198768           -19.1%   37355723        unixbench.workload
>  1.365e+08           -12.5%  1.195e+08 ±  7%  cpuidle..usage
>    1220612 ±  4%     -38.0%     757009 ± 28%  meminfo.Active
>    1220354 ±  4%     -38.0%     756754 ± 28%  meminfo.Active(anon)
>       0.50 ±  2%      -0.1        0.45 ±  4%  mpstat.cpu.all.soft%
>       1.73            -0.2        1.52 ±  2%  mpstat.cpu.all.usr%
>     532266           -18.4%     434559        vmstat.system.cs
>     495826           -12.2%     435455 ±  8%  vmstat.system.in
>   1.36e+08           -13.2%   1.18e+08 ±  9%  turbostat.C1
>      68.80            +0.8       69.60        turbostat.C1%
>  1.663e+08           -12.1%  1.462e+08 ±  8%  turbostat.IRQ
>      15.54 ± 20%     -49.0%       7.93 ± 24%  sched_debug.cfs_rq:/.runnable_avg.min
>      13.26 ± 19%     -46.6%       7.08 ± 29%  sched_debug.cfs_rq:/.util_avg.min
>      48.96 ±  8%     +51.5%      74.20 ± 13%  sched_debug.cfs_rq:/.util_est_enqueued.avg
>     138.00 ±  5%     +28.9%     177.87 ±  7%  sched_debug.cfs_rq:/.util_est_enqueued.stddev
>     228060 ±  3%     +13.3%     258413 ±  4%  sched_debug.cpu.avg_idle.stddev
>     432533 ±  5%     -16.4%     361517 ±  4%  sched_debug.cpu.nr_switches.min
>  2.665e+08           -18.9%  2.162e+08        numa-numastat.node0.local_node
>  2.666e+08           -18.9%  2.163e+08        numa-numastat.node0.numa_hit
>  2.746e+08           -20.9%  2.172e+08        numa-numastat.node1.local_node
>  2.747e+08           -20.9%  2.172e+08        numa-numastat.node1.numa_hit
>  2.602e+08           -17.4%  2.149e+08        numa-numastat.node2.local_node
>  2.603e+08           -17.4%  2.149e+08        numa-numastat.node2.numa_hit
>  2.423e+08           -15.0%   2.06e+08        numa-numastat.node3.local_node
>  2.424e+08           -15.0%  2.061e+08        numa-numastat.node3.numa_hit

So we're going off-node a lot more for ... something.

>  2.666e+08           -18.9%  2.163e+08        numa-vmstat.node0.numa_hit
>  2.665e+08           -18.9%  2.162e+08        numa-vmstat.node0.numa_local
>  2.747e+08           -20.9%  2.172e+08        numa-vmstat.node1.numa_hit
>  2.746e+08           -20.9%  2.172e+08        numa-vmstat.node1.numa_local
>  2.603e+08           -17.4%  2.149e+08        numa-vmstat.node2.numa_hit
>  2.602e+08           -17.4%  2.149e+08        numa-vmstat.node2.numa_local
>  2.424e+08           -15.0%  2.061e+08        numa-vmstat.node3.numa_hit
>  2.423e+08           -15.0%   2.06e+08        numa-vmstat.node3.numa_local
>     304947 ±  4%     -38.0%     189144 ± 28%  proc-vmstat.nr_active_anon

Umm.  Are we running vmstat a lot during this test?  The commit says:

    At the
    moment the readers are either procfs interface, oom_killer and memory
    reclaim which I think are not performance critical and should be ok with
    slow read.  However I think we can make that change in a separate patch.

This would explain the increased cross-NUMA references (we're going to
the other nodes to collect the stats), and the general slowdown.  But I
don't think it reflects a real workload; it's reflecting that the
monitoring of this workload that we're doing is now more accurate and
more expensive.