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 >
