lkml.org 
[lkml]   [2021]   [Jul]   [2]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    SubjectRe: [RFC v2 00/34] SLUB: reduce irq disabled scope and make it RT compatible
    From
    Date
    On 7/2/21 8:29 PM, 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):

    Thanks for testing!

    > - A "time make -j32" run of allmodconfig on /dev/shm.
    > Old:
    > | real 20m6,217s
    > | user 568m22,553s
    > | sys 48m33,126s
    >
    > New:
    > | real 20m9,049s
    > | user 569m32,096s
    > | sys 48m47,670s
    >
    > These 3 seconds here are probably in the noise range.
    >
    > - perf_5.10 stat -r 10 hackbench -g200 -s 4096 -l500
    > Old:
    > | 464.967,20 msec task-clock # 27,220 CPUs utilized ( +- 0,16% )
    > | 7.683.944 context-switches # 0,017 M/sec ( +- 0,86% )
    > | 931.380 cpu-migrations # 0,002 M/sec ( +- 4,94% )
    > | 219.569 page-faults # 0,472 K/sec ( +- 0,39% )
    > | 1.104.727.599.918 cycles # 2,376 GHz ( +- 0,18% )
    > | 941.428.898.087 stalled-cycles-frontend # 85,22% frontend cycles idle ( +- 0,24% )
    > | 729.016.546.572 stalled-cycles-backend # 65,99% backend cycles idle ( +- 0,32% )
    > | 340.133.571.519 instructions # 0,31 insn per cycle
    > | # 2,77 stalled cycles per insn ( +- 0,12% )
    > | 73.746.821.314 branches # 158,607 M/sec ( +- 0,13% )
    > | 377.838.006 branch-misses # 0,51% of all branches ( +- 1,01% )
    > |
    > | 17,0820 +- 0,0202 seconds time elapsed ( +- 0,12% )
    >
    > New:
    > | 422.865,71 msec task-clock # 4,782 CPUs utilized ( +- 0,34% )
    > | 14.594.238 context-switches # 0,035 M/sec ( +- 0,43% )
    > | 3.737.926 cpu-migrations # 0,009 M/sec ( +- 0,46% )
    > | 218.474 page-faults # 0,517 K/sec ( +- 0,74% )
    > | 940.715.812.020 cycles # 2,225 GHz ( +- 0,34% )
    > | 716.593.827.820 stalled-cycles-frontend # 76,18% frontend cycles idle ( +- 0,39% )
    > | 550.730.862.839 stalled-cycles-backend # 58,54% backend cycles idle ( +- 0,43% )
    > | 417.274.588.907 instructions # 0,44 insn per cycle
    > | # 1,72 stalled cycles per insn ( +- 0,17% )
    > | 92.814.150.290 branches # 219,488 M/sec ( +- 0,17% )
    > | 822.102.170 branch-misses # 0,89% of all branches ( +- 0,41% )
    > |
    > | 88,427 +- 0,618 seconds time elapsed ( +- 0,70% )
    >
    > So this is outside of the noise range.
    > I'm not sure where this is coming from. My guess would be higher lock
    > contention within the memory allocator.

    The series shouldn't significantly change the memory allocator
    interaction, though.
    Seems there's less cycles, but more time elapsed, thus more sleeping -
    is it locks becoming mutexes on RT?

    My first guess - the last, local_lock patch. What would happen if you
    take that one out? Should be still RT-compatible. If it improves a lot,
    maybe that conversion to local_lock is not worth it then.

    My second guess - list_lock remains spinlock with my series, thus RT
    mutex, but the current RT tree converts it to raw_spinlock. I'd hope
    leaving that one as non-raw spinlock would still be much better for RT
    goals, even if hackbench (which is AFAIK very slab intensive) throughput
    regresses - hopefully not that much.

    >> The remaining patches to upstream from the RT tree are small ones related to
    >> KConfig. The patch that restricts PREEMPT_RT to SLUB (not SLAB or SLOB) makes
    >> sense. The patch that disables CONFIG_SLUB_CPU_PARTIAL with PREEMPT_RT could
    >> perhaps be re-evaluated as the series also addresses some latency issues with
    >> percpu partial slabs.
    >
    > With that series the PARTIAL slab can be indeed enabled. I have (had) a
    > half done series where I had PARTIAL enabled and noticed a slight
    > increase in latency so made it "default y on !RT". It wasn't dramatic
    > but appeared to be outside of noise.
    >
    > Sebastian
    >

    \
     
     \ /
      Last update: 2021-07-02 22:26    [W:3.256 / U:27.248 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site