> > On 12/6/2018 4:28 PM, Steve Sistare wrote: >> When a CPU has no more CFS tasks to run, and idle_balance() fails to >> find a task, then attempt to steal a task from an overloaded CPU in the >> same LLC. Maintain and use a bitmap of overloaded CPUs to efficiently >> identify candidates. To minimize search time, steal the first migratable >> task that is found when the bitmap is traversed. For fairness, search >> for migratable tasks on an overloaded CPU in order of next to run. >> >> This simple stealing yields a higher CPU utilization than idle_balance() >> alone, because the search is cheap, so it may be called every time the CPU >> is about to go idle. idle_balance() does more work because it searches >> widely for the busiest queue, so to limit its CPU consumption, it declines >> to search if the system is too busy. Simple stealing does not offload the >> globally busiest queue, but it is much better than running nothing at all. >> >> The bitmap of overloaded CPUs is a new type of sparse bitmap, designed to >> reduce cache contention vs the usual bitmap when many threads concurrently >> set, clear, and visit elements. >> >> Patch 1 defines the sparsemask type and its operations. >> >> Patches 2, 3, and 4 implement the bitmap of overloaded CPUs. >> >> Patches 5 and 6 refactor existing code for a cleaner merge of later >> patches. >> >> Patches 7 and 8 implement task stealing using the overloaded CPUs bitmap. >> >> Patch 9 disables stealing on systems with more than 2 NUMA nodes for the >> time being because of performance regressions that are not due to stealing >> per-se. See the patch description for details. >> >> Patch 10 adds schedstats for comparing the new behavior to the old, and >> provided as a convenience for developers only, not for integration. >> >> The patch series is based on kernel 4.20.0-rc1. It compiles, boots, and >> runs with/without each of CONFIG_SCHED_SMT, CONFIG_SMP, CONFIG_SCHED_DEBUG, >> and CONFIG_PREEMPT. It runs without error with CONFIG_DEBUG_PREEMPT + >> CONFIG_SLUB_DEBUG + CONFIG_DEBUG_PAGEALLOC + CONFIG_DEBUG_MUTEXES + >> CONFIG_DEBUG_SPINLOCK + CONFIG_DEBUG_ATOMIC_SLEEP. CPU hot plug and CPU >> bandwidth control were tested. >> >> Stealing improves utilization with only a modest CPU overhead in scheduler >> code. In the following experiment, hackbench is run with varying numbers >> of groups (40 tasks per group), and the delta in /proc/schedstat is shown >> for each run, averaged per CPU, augmented with these non-standard stats: >> >> %find - percent of time spent in old and new functions that search for >> idle CPUs and tasks to steal and set the overloaded CPUs bitmap. >> >> steal - number of times a task is stolen from another CPU. >> >> X6-2: 1 socket * 10 cores * 2 hyperthreads = 20 CPUs >> Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz >> hackbench <grps> process 100000 >> sched_wakeup_granularity_ns=15000000 >> >> baseline >> grps time %busy slice sched idle wake %find steal >> 1 8.084 75.02 0.10 105476 46291 59183 0.31 0 >> 2 13.892 85.33 0.10 190225 70958 119264 0.45 0 >> 3 19.668 89.04 0.10 263896 87047 176850 0.49 0 >> 4 25.279 91.28 0.10 322171 94691 227474 0.51 0 >> 8 47.832 94.86 0.09 630636 144141 486322 0.56 0 >> >> new >> grps time %busy slice sched idle wake %find steal %speedup >> 1 5.938 96.80 0.24 31255 7190 24061 0.63 7433 36.1 >> 2 11.491 99.23 0.16 74097 4578 69512 0.84 19463 20.9 >> 3 16.987 99.66 0.15 115824 1985 113826 0.77 24707 15.8 >> 4 22.504 99.80 0.14 167188 2385 164786 0.75 29353 12.3 >> 8 44.441 99.86 0.11 389153 1616 387401 0.67 38190 7.6 >> >> Elapsed time improves by 8 to 36%, and CPU busy utilization is up >> by 5 to 22% hitting 99% for 2 or more groups (80 or more tasks). >> The cost is at most 0.4% more find time. >> >> Additional performance results follow. A negative "speedup" is a >> regression. Note: for all hackbench runs, sched_wakeup_granularity_ns >> is set to 15 msec. Otherwise, preemptions increase at higher loads and >> distort the comparison between baseline and new. >> >> ------------------ 1 Socket Results ------------------ >> >> X6-2: 1 socket * 10 cores * 2 hyperthreads = 20 CPUs >> Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz >> Average of 10 runs of: hackbench <groups> process 100000 >> >> --- base -- --- new --- >> groups time %stdev time %stdev %speedup >> 1 8.008 0.1 5.905 0.2 35.6 >> 2 13.814 0.2 11.438 0.1 20.7 >> 3 19.488 0.2 16.919 0.1 15.1 >> 4 25.059 0.1 22.409 0.1 11.8 >> 8 47.478 0.1 44.221 0.1 7.3 >> >> X6-2: 1 socket * 22 cores * 2 hyperthreads = 44 CPUs >> Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz >> Average of 10 runs of: hackbench <groups> process 100000 >> >> --- base -- --- new --- >> groups time %stdev time %stdev %speedup >> 1 4.586 0.8 4.596 0.6 -0.3 >> 2 7.693 0.2 5.775 1.3 33.2 >> 3 10.442 0.3 8.288 0.3 25.9 >> 4 13.087 0.2 11.057 0.1 18.3 >> 8 24.145 0.2 22.076 0.3 9.3 >> 16 43.779 0.1 41.741 0.2 4.8 >> >> KVM 4-cpu >> Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz >> tbench, average of 11 runs. >> >> clients %speedup >> 1 16.2 >> 2 11.7 >> 4 9.9 >> 8 12.8 >> 16 13.7 >> >> KVM 2-cpu >> Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz >> >> Benchmark %speedup >> specjbb2015_critical_jops 5.7 >> mysql_sysb1.0.14_mutex_2 40.6 >> mysql_sysb1.0.14_oltp_2 3.9 >> >> ------------------ 2 Socket Results ------------------ >> >> X6-2: 2 sockets * 10 cores * 2 hyperthreads = 40 CPUs >> Intel(R) Xeon(R) CPU E5-2630 v4 @ 2.20GHz >> Average of 10 runs of: hackbench <groups> process 100000 >> >> --- base -- --- new --- >> groups time %stdev time %stdev %speedup >> 1 7.945 0.2 7.219 8.7 10.0 >> 2 8.444 0.4 6.689 1.5 26.2 >> 3 12.100 1.1 9.962 2.0 21.4 >> 4 15.001 0.4 13.109 1.1 14.4 >> 8 27.960 0.2 26.127 0.3 7.0 >> >> X6-2: 2 sockets * 22 cores * 2 hyperthreads = 88 CPUs >> Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz >> Average of 10 runs of: hackbench <groups> process 100000 >> >> --- base -- --- new --- >> groups time %stdev time %stdev %speedup >> 1 5.826 5.4 5.840 5.0 -0.3 >> 2 5.041 5.3 6.171 23.4 -18.4 >> 3 6.839 2.1 6.324 3.8 8.1 >> 4 8.177 0.6 7.318 3.6 11.7 >> 8 14.429 0.7 13.966 1.3 3.3 >> 16 26.401 0.3 25.149 1.5 4.9 >> >> >> X6-2: 2 sockets * 22 cores * 2 hyperthreads = 88 CPUs >> Intel(R) Xeon(R) CPU E5-2699 v4 @ 2.20GHz >> Oracle database OLTP, logging disabled, NVRAM storage >> >> Customers Users %speedup >> 1200000 40 -1.2 >> 2400000 80 2.7 >> 3600000 120 8.9 >> 4800000 160 4.4 >> 6000000 200 3.0 >> >> X6-2: 2 sockets * 14 cores * 2 hyperthreads = 56 CPUs >> Intel(R) Xeon(R) CPU E5-2690 v4 @ 2.60GHz >> Results from the Oracle "Performance PIT". >> >> Benchmark %speedup >> >> mysql_sysb1.0.14_fileio_56_rndrd 19.6 >> mysql_sysb1.0.14_fileio_56_seqrd 12.1 >> mysql_sysb1.0.14_fileio_56_rndwr 0.4 >> mysql_sysb1.0.14_fileio_56_seqrewr -0.3 >> >> pgsql_sysb1.0.14_fileio_56_rndrd 19.5 >> pgsql_sysb1.0.14_fileio_56_seqrd 8.6 >> pgsql_sysb1.0.14_fileio_56_rndwr 1.0 >> pgsql_sysb1.0.14_fileio_56_seqrewr 0.5 >> >> opatch_time_ASM_12.2.0.1.0_HP2M 7.5 >> select-1_users-warm_asmm_ASM_12.2.0.1.0_HP2M 5.1 >> select-1_users_asmm_ASM_12.2.0.1.0_HP2M 4.4 >> swingbenchv3_asmm_soebench_ASM_12.2.0.1.0_HP2M 5.8 >> >> lm3_memlat_L2 4.8 >> lm3_memlat_L1 0.0 >> >> ub_gcc_56CPUs-56copies_Pipe-based_Context_Switching 60.1 >> ub_gcc_56CPUs-56copies_Shell_Scripts_1_concurrent 5.2 >> ub_gcc_56CPUs-56copies_Shell_Scripts_8_concurrent -3.0 >> ub_gcc_56CPUs-56copies_File_Copy_1024_bufsize_2000_maxblocks 2.4 >> >> X5-2: 2 sockets * 18 cores * 2 hyperthreads = 72 CPUs >> Intel(R) Xeon(R) CPU E5-2699 v3 @ 2.30GHz >> >> NAS_OMP >> bench class ncpu %improved(Mops) >> dc B 72 1.3 >> is C 72 0.9 >> is D 72 0.7 >> >> sysbench mysql, average of 24 runs >> --- base --- --- new --- >> nthr events %stdev events %stdev %speedup >> 1 331.0 0.25 331.0 0.24 -0.1 >> 2 661.3 0.22 661.8 0.22 0.0 >> 4 1297.0 0.88 1300.5 0.82 0.2 >> 8 2420.8 0.04 2420.5 0.04 -0.1 >> 16 4826.3 0.07 4825.4 0.05 -0.1 >> 32 8815.3 0.27 8830.2 0.18 0.1 >> 64 12823.0 0.24 12823.6 0.26 0.0 >> >> -------------------------------------------------------------- >> >> Changes from v1 to v2: >> - Remove stray find_time hunk from patch 5 >> - Fix "warning: label out defined but not used" for !CONFIG_SCHED_SMT >> - Set SCHED_STEAL_NODE_LIMIT_DEFAULT to 2 >> - Steal iff avg_idle exceeds the cost of stealing >> >> Changes from v2 to v3: >> - Update series for kernel 4.20. Context changes only. >> >> Changes from v3 to v4: >> - Avoid 64-bit division on 32-bit processors in compute_skid() >> - Replace IF_SMP with inline functions to set idle_stamp >> - Push ZALLOC_MASK body into calling function >> - Set rq->cfs_overload_cpus in update_top_cache_domain instead of >> cpu_attach_domain >> - Rewrite sparsemask iterator for complete inlining >> - Cull and clean up sparsemask functions and moved all into >> sched/sparsemask.h >> >> Steve Sistare (10): >> sched: Provide sparsemask, a reduced contention bitmap >> sched/topology: Provide hooks to allocate data shared per LLC >> sched/topology: Provide cfs_overload_cpus bitmap >> sched/fair: Dynamically update cfs_overload_cpus >> sched/fair: Hoist idle_stamp up from idle_balance >> sched/fair: Generalize the detach_task interface >> sched/fair: Provide can_migrate_task_llc >> sched/fair: Steal work from an overloaded CPU when CPU goes idle >> sched/fair: disable stealing if too many NUMA nodes >> sched/fair: Provide idle search schedstats >> >> include/linux/sched/topology.h | 1 + >> kernel/sched/core.c | 31 +++- >> kernel/sched/fair.c | 354 >> +++++++++++++++++++++++++++++++++++++---- >> kernel/sched/features.h | 6 + >> kernel/sched/sched.h | 13 +- >> kernel/sched/sparsemask.h | 210 ++++++++++++++++++++++++ >> kernel/sched/stats.c | 11 +- >> kernel/sched/stats.h | 13 ++ >> kernel/sched/topology.c | 121 +++++++++++++- >> 9 files changed, 726 insertions(+), 34 deletions(-) >> create mode 100644 kernel/sched/sparsemask.h >>
On 2019-01-14 8:55 a.m., Steven Sistare wrote:> Hi Peter and Ingo, > I am waiting for one of you to review, ack, or reject this series. I > have addressed all known issues. I have a reviewed-by from Valentin > and a > tested-by from Vincent which I will add to v5 if you approve the > patch. > Hi Thomas, Peter, Ingo, These patches have been around for a bit and have been reviewed by others. Could one of you please take a look at them, and let us know if we are heading in the right direction? Dhaval
