Re: [PATCH 3/4] mm/memcg: Add a local_lock_t for IRQ and TASK object.

[Sebastian Andrzej Siewior <bigeasy@linutronix.de>]

On 2022-02-01 16:29:35 [+0100], Michal Hocko wrote:
> > > Sorry, I know that this all is not really related to your work but if
> > > the original optimization is solely based on artificial benchmarks then
> > > I would rather drop it and also make your RT patchset easier.
> > 
> > Do you have any real-world benchmark in mind? Like something that is
> > already used for testing/ benchmarking and would fit here?
> 
> Anything that even remotely resembles a real allocation heavy workload.

So I figured out that build the kernel as user triggers the allocation
path in_task() and in_interrupt(). I booted a PREEMPT_NONE kernel and
run "perf stat -r 5 b.sh" where b.sh unpacks a kernel and runs a
allmodconfig build on /dev/shm. The slow disk should not be a problem.

With the optimisation:
|  Performance counter stats for './b.sh' (5 runs):
| 
|       43.367.405,59 msec task-clock                #   30,901 CPUs utilized            ( +-  0,01% )
|           7.393.238      context-switches          #  170,499 /sec                     ( +-  0,13% )
|             832.364      cpu-migrations            #   19,196 /sec                     ( +-  0,15% )
|         625.235.644      page-faults               #   14,419 K/sec                    ( +-  0,00% )
| 103.822.081.026.160      cycles                    #    2,394 GHz                      ( +-  0,01% )
|  75.392.684.840.822      stalled-cycles-frontend   #   72,63% frontend cycles idle     ( +-  0,02% )
|  54.971.177.787.990      stalled-cycles-backend    #   52,95% backend cycles idle      ( +-  0,02% )
|  69.543.893.308.966      instructions              #    0,67  insn per cycle
|                                                    #    1,08  stalled cycles per insn  ( +-  0,00% )
|  14.585.269.354.314      branches                  #  336,357 M/sec                    ( +-  0,00% )
|     558.029.270.966      branch-misses             #    3,83% of all branches          ( +-  0,01% )
|  
|            1403,441 +- 0,466 seconds time elapsed  ( +-  0,03% )


With the optimisation disabled:
|  Performance counter stats for './b.sh' (5 runs):
| 
|       43.354.742,31 msec task-clock                #   30,869 CPUs utilized            ( +-  0,01% )
|           7.394.210      context-switches          #  170,601 /sec                     ( +-  0,06% )
|             842.835      cpu-migrations            #   19,446 /sec                     ( +-  0,63% )
|         625.242.341      page-faults               #   14,426 K/sec                    ( +-  0,00% )
| 103.791.714.272.978      cycles                    #    2,395 GHz                      ( +-  0,01% )
|  75.369.652.256.425      stalled-cycles-frontend   #   72,64% frontend cycles idle     ( +-  0,01% )
|  54.947.610.706.450      stalled-cycles-backend    #   52,96% backend cycles idle      ( +-  0,01% )
|  69.529.388.440.691      instructions              #    0,67  insn per cycle
|                                                    #    1,08  stalled cycles per insn  ( +-  0,01% )
|  14.584.515.016.870      branches                  #  336,497 M/sec                    ( +-  0,00% )
|     557.716.885.609      branch-misses             #    3,82% of all branches          ( +-  0,02% )
|  
|             1404,47 +- 1,05 seconds time elapsed  ( +-  0,08% )

I'm still open to a more specific test ;)

Sebastian