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

- 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 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

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