Re: [memcg] a8c49af3be: hackbench.throughput -13.7% regression

[Yin Fengwei <fengwei.yin@intel.com>]

Hi Yosry,

On 4/20/2022 1:58 PM, kernel test robot wrote:
> 
> 
> Greeting,
> 
> FYI, we noticed a -13.7% regression of hackbench.throughput due to commit:
> 
> 
> commit: a8c49af3be5f0b4e105ef678bcf14ef102c270be ("memcg: add per-memcg total kernel memory stat")
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git master
> 
> in testcase: hackbench
> on test machine: 144 threads 4 sockets Intel(R) Xeon(R) Gold 5318H CPU @ 2.50GHz with 128G memory
> with following parameters:
> 
> 	nr_threads: 100%
> 	iterations: 4
> 	mode: process
> 	ipc: socket
> 	cpufreq_governor: performance
> 	ucode: 0x7002402
> 
> test-description: Hackbench is both a benchmark and a stress test for the Linux kernel scheduler.
> test-url: https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/sched/cfs-scheduler/hackbench.c
> 
> 
> 
> If you fix the issue, kindly add following tag
> Reported-by: kernel test robot <oliver.sang@intel.com>
> 
> 
> 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/ucode:
>   gcc-11/performance/socket/4/x86_64-rhel-8.3/process/100%/debian-10.4-x86_64-20200603.cgz/lkp-cpl-4sp1/hackbench/0x7002402
> 
> commit: 
>   086f694a75 ("memcg: replace in_interrupt() with !in_task()")
>   a8c49af3be ("memcg: add per-memcg total kernel memory stat")
> 
> 086f694a75e1a283 a8c49af3be5f0b4e105ef678bcf 
> ---------------- --------------------------- 
>          %stddev     %change         %stddev
>              \          |                \  
>     146519           -13.7%     126397        hackbench.throughput
>     465.89           +16.0%     540.43        hackbench.time.elapsed_time
>     465.89           +16.0%     540.43        hackbench.time.elapsed_time.max
>  1.365e+08          +134.1%  3.195e+08 ±  4%  hackbench.time.involuntary_context_switches
>    1081515            -1.2%    1068489        hackbench.time.minor_page_faults
>      64911           +16.3%      75465        hackbench.time.system_time

Just FYI.

If I comment out one line added by the commit <a8c49af3be> :
static void memcg_account_kmem(struct mem_cgroup *memcg, int nr_pages)
{
        /* mod_memcg_state(memcg, MEMCG_KMEM, nr_pages); */  <--- comment out this line.
        if (!cgroup_subsys_on_dfl(memory_cgrp_subsys)) {
                if (nr_pages > 0)
                        page_counter_charge(&memcg->kmem, nr_pages);
                else
                        page_counter_uncharge(&memcg->kmem, -nr_pages);
        }
}

The regression is almost gone:

086f694a75e1a283 9ff9ec89a6dcf39f901ff0a84fd
---------------- ---------------------------
       fail:runs  %reproduction    fail:runs
           |             |             |
       7632:13      -44932%        1791:3     dmesg.timestamp:last
          1:13          -8%            :3     kmsg.common_interrupt:#No_irq_handler_for_vector
          2:13         -20%            :3     kmsg.timestamp:common_interrupt:#No_irq_handler_for_vector
       4072:13      -24827%         844:3     kmsg.timestamp:last
         %stddev     %change         %stddev
             \          |                \
    144327 ±  3%      -1.9%     141594 ±  5%  hackbench.throughput
                      regression dropped to -1.9% from -13.7%

    473.44 ±  3%      +1.9%     482.23 ±  5%  hackbench.time.elapsed_time


Regards
Yin, Fengwei