Re: [RFC v2 00/34] SLUB: reduce irq disabled scope and make it RT compatible

[Mike Galbraith]

On Fri, 2021-07-02 at 20:29 +0200, Sebastian Andrzej Siewior wrote:
> I replaced my slub changes with slub-local-lock-v2r3.
> I haven't seen any complains from lockdep or so which is good. Then I
> did this with RT enabled (and no debug):

Below is some raw hackbench data from my little i4790 desktop box.  It
says we'll definitely still want list_lock to be raw.

It also appears to be saying that there's something RT specific to
stare at in addition to the list_lock business, but add a pinch of salt
to that due to the config of the virgin(ish) tip tree being much
lighter than the enterprise(ish) config of the tip-rt tree.

perf stat -r10 hackbench -s4096 -l500
full warmup, record, repeat twice for elapsed

5.13.0.g60ab3ed-tip-rt
          8,898.51 msec task-clock                #    7.525 CPUs utilized            ( +-  0.33% )
           368,922      context-switches          #    0.041 M/sec                    ( +-  5.20% )
            42,281      cpu-migrations            #    0.005 M/sec                    ( +-  5.28% )
            13,180      page-faults               #    0.001 M/sec                    ( +-  0.70% )
    33,343,378,867      cycles                    #    3.747 GHz                      ( +-  0.30% )
    21,656,783,887      instructions              #    0.65  insn per cycle           ( +-  0.67% )
     4,408,569,663      branches                  #  495.428 M/sec                    ( +-  0.73% )
        12,040,125      branch-misses             #    0.27% of all branches          ( +-  2.93% )

           1.18260 +- 0.00473 seconds time elapsed  ( +-  0.40% )
           1.19018 +- 0.00441 seconds time elapsed  ( +-  0.37% ) (repeat)
           1.18260 +- 0.00473 seconds time elapsed  ( +-  0.40% ) (repeat)

5.13.0.g60ab3ed-tip-rt +slub-local-lock-v2r3 list_lock=raw_spinlock_t
          9,642.00 msec task-clock                #    7.521 CPUs utilized            ( +-  0.46% )
           462,091      context-switches          #    0.048 M/sec                    ( +-  4.79% )
            44,411      cpu-migrations            #    0.005 M/sec                    ( +-  4.34% )
            12,980      page-faults               #    0.001 M/sec                    ( +-  0.43% )
    36,098,859,429      cycles                    #    3.744 GHz                      ( +-  0.44% )
    25,462,853,462      instructions              #    0.71  insn per cycle           ( +-  0.50% )
     5,260,898,360      branches                  #  545.623 M/sec                    ( +-  0.52% )
        16,088,686      branch-misses             #    0.31% of all branches          ( +-  2.02% )

           1.28207 +- 0.00568 seconds time elapsed  ( +-  0.44% )
           1.28744 +- 0.00713 seconds time elapsed  ( +-  0.55% ) (repeat)
           1.28085 +- 0.00850 seconds time elapsed  ( +-  0.66% ) (repeat)

5.13.0.g60ab3ed-tip-rt +slub-local-lock-v2r3 list_lock=spinlock_t
         10,004.89 msec task-clock                #    6.029 CPUs utilized            ( +-  1.37% )
           654,311      context-switches          #    0.065 M/sec                    ( +-  5.16% )
           211,070      cpu-migrations            #    0.021 M/sec                    ( +-  1.38% )
            13,262      page-faults               #    0.001 M/sec                    ( +-  0.79% )
    36,585,914,931      cycles                    #    3.657 GHz                      ( +-  1.35% )
    27,682,240,511      instructions              #    0.76  insn per cycle           ( +-  1.06% )
     5,766,064,432      branches                  #  576.325 M/sec                    ( +-  1.11% )
        24,269,069      branch-misses             #    0.42% of all branches          ( +-  2.03% )

            1.6595 +- 0.0116 seconds time elapsed  ( +-  0.70% )
            1.6270 +- 0.0180 seconds time elapsed  ( +-  1.11% ) (repeat)
            1.6213 +- 0.0150 seconds time elapsed  ( +-  0.93% ) (repeat)

virgin(ish) tip
5.13.0.g60ab3ed-tip
          7,320.67 msec task-clock                #    7.792 CPUs utilized            ( +-  0.31% )
           221,215      context-switches          #    0.030 M/sec                    ( +-  3.97% )
            16,234      cpu-migrations            #    0.002 M/sec                    ( +-  4.07% )
            13,233      page-faults               #    0.002 M/sec                    ( +-  0.91% )
    27,592,205,252      cycles                    #    3.769 GHz                      ( +-  0.32% )
     8,309,495,040      instructions              #    0.30  insn per cycle           ( +-  0.37% )
     1,555,210,607      branches                  #  212.441 M/sec                    ( +-  0.42% )
         5,484,209      branch-misses             #    0.35% of all branches          ( +-  2.13% )

           0.93949 +- 0.00423 seconds time elapsed  ( +-  0.45% )
           0.94608 +- 0.00384 seconds time elapsed  ( +-  0.41% ) (repeat)
           0.94422 +- 0.00410 seconds time elapsed  ( +-  0.43% )

5.13.0.g60ab3ed-tip +slub-local-lock-v2r3
          7,343.57 msec task-clock                #    7.776 CPUs utilized            ( +-  0.44% )
           223,044      context-switches          #    0.030 M/sec                    ( +-  3.02% )
            16,057      cpu-migrations            #    0.002 M/sec                    ( +-  4.03% )
            13,164      page-faults               #    0.002 M/sec                    ( +-  0.97% )
    27,684,906,017      cycles                    #    3.770 GHz                      ( +-  0.45% )
     8,323,273,871      instructions              #    0.30  insn per cycle           ( +-  0.28% )
     1,556,106,680      branches                  #  211.901 M/sec                    ( +-  0.31% )
         5,463,468      branch-misses             #    0.35% of all branches          ( +-  1.33% )

           0.94440 +- 0.00352 seconds time elapsed  ( +-  0.37% )
           0.94830 +- 0.00228 seconds time elapsed  ( +-  0.24% ) (repeat)
           0.93813 +- 0.00440 seconds time elapsed  ( +-  0.47% ) (repeat)