Current select_idle_sibling first tries to find a fully idle core using select_idle_core which can potentially search all cores and if it fails it finds any idle cpu using select_idle_cpu. select_idle_cpu can potentially search all cpus in the llc domain. This doesn't scale for large llc domains and will only get worse with more cores in future.
This patch solves the scalability problem by: - Setting an upper and lower limit of idle cpu search in select_idle_cpu to keep search time low and constant - Adding a new sched feature SIS_CORE to disable select_idle_core Additionally it also introduces a new per-cpu variable next_cpu to track the limit of search so that every time search starts from where it ended. This rotating search window over cpus in LLC domain ensures that idle cpus are eventually found in case of high load. Following are the performance numbers with various benchmarks with SIS_CORE true (idle core search enabled). Hackbench process on 2 socket, 44 core and 88 threads Intel x86 machine (lower is better): groups baseline %stdev patch %stdev 1 0.5816 8.94 0.5903 (-1.5%) 11.28 2 0.6428 10.64 0.5843 (9.1%) 4.93 4 1.0152 1.99 0.9965 (1.84%) 1.83 8 1.8128 1.4 1.7921 (1.14%) 1.76 16 3.1666 0.8 3.1345 (1.01%) 0.81 32 5.6084 0.83 5.5677 (0.73%) 0.8 Sysbench MySQL on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): threads baseline %stdev patch %stdev 8 2095.45 1.82 2102.6 (0.34%) 2.11 16 4218.45 0.06 4221.35 (0.07%) 0.38 32 7531.36 0.49 7607.18 (1.01%) 0.25 48 10206.42 0.21 10324.26 (1.15%) 0.13 64 12053.73 0.1 12158.3 (0.87%) 0.24 128 14810.33 0.04 14840.4 (0.2%) 0.38 Oracle DB on 2 socket, 44 core and 88 threads Intel x86 machine (normalized, higher is better): users baseline %stdev patch %stdev 20 1 0.9 1.0068 (0.68%) 0.27 40 1 0.8 1.0103 (1.03%) 1.24 60 1 0.34 1.0178 (1.78%) 0.49 80 1 0.53 1.0092 (0.92%) 1.5 100 1 0.79 1.0090 (0.9%) 0.88 120 1 0.06 1.0048 (0.48%) 0.72 140 1 0.22 1.0116 (1.16%) 0.05 160 1 0.57 1.0264 (2.64%) 0.67 180 1 0.81 1.0194 (1.94%) 0.91 200 1 0.44 1.028 (2.8%) 3.09 220 1 1.74 1.0229 (2.29%) 0.21 Uperf pingpong on 2 socket, 44 core and 88 threads Intel x86 machine with message size = 8k (higher is better): threads baseline %stdev patch %stdev 8 45.36 0.43 46.28 (2.01%) 0.29 16 87.81 0.82 89.67 (2.12%) 0.38 32 151.19 0.02 153.5 (1.53%) 0.41 48 190.2 0.21 194.79 (2.41%) 0.07 64 190.42 0.35 202.9 (6.55%) 1.66 128 323.86 0.28 343.56 (6.08%) 1.34 Dbench on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): clients baseline patch 1 629.8 603.83 (-4.12%) 2 1159.65 1155.75 (-0.34%) 4 2121.61 2093.99 (-1.3%) 8 2620.52 2641.51 (0.8%) 16 2879.31 2897.6 (0.64%) Tbench on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): clients baseline patch 1 256.41 255.8 (-0.24%) 2 509.89 504.52 (-1.05%) 4 999.44 1003.74 (0.43%) 8 1982.7 1976.42 (-0.32%) 16 3891.51 3916.04 (0.63%) 32 6819.24 6845.06 (0.38%) 64 8542.95 8568.28 (0.3%) 128 15277.6 15754.6 (3.12%) Schbench on 2 socket, 44 core and 88 threads Intel x86 machine with 44 tasks (lower is better): percentile baseline %stdev patch %stdev 50 94 2.82 92 (2.13%) 2.17 75 124 2.13 122 (1.61%) 1.42 90 152 1.74 151 (0.66%) 0.66 95 171 2.11 170 (0.58%) 0 99 512.67 104.96 208.33 (59.36%) 1.2 99.5 2296 82.55 3674.66 (-60.05%) 22.19 99.9 12517.33 2.38 12784 (-2.13%) 0.66 Hackbench process on 2 socket, 16 core and 128 threads SPARC machine (lower is better): groups baseline %stdev patch %stdev 1 1.3085 6.65 1.2213 (6.66%) 10.32 2 1.4559 8.55 1.5048 (-3.36%) 4.72 4 2.6271 1.74 2.5532 (2.81%) 2.02 8 4.7089 3.01 4.5118 (4.19%) 2.74 16 8.7406 2.25 8.6801 (0.69%) 4.78 32 17.7835 1.01 16.759 (5.76%) 1.38 64 36.1901 0.65 34.6652 (4.21%) 1.24 128 72.6585 0.51 70.9762 (2.32%) 0.9 Following are the performance numbers with various benchmarks with SIS_CORE false (idle core search disabled). This improves throughput of certain workloads but increases latency of other workloads. Hackbench process on 2 socket, 44 core and 88 threads Intel x86 machine (lower is better): groups baseline %stdev patch %stdev 1 0.5816 8.94 0.5835 (-0.33%) 8.21 2 0.6428 10.64 0.5752 (10.52%) 4.05 4 1.0152 1.99 0.9946 (2.03%) 2.56 8 1.8128 1.4 1.7619 (2.81%) 1.88 16 3.1666 0.8 3.1275 (1.23%) 0.42 32 5.6084 0.83 5.5856 (0.41%) 0.89 Sysbench MySQL on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): threads baseline %stdev patch %stdev 8 2095.45 1.82 2084.72 (-0.51%) 1.65 16 4218.45 0.06 4179.69 (-0.92%) 0.18 32 7531.36 0.49 7623.18 (1.22%) 0.39 48 10206.42 0.21 10159.16 (-0.46%) 0.21 64 12053.73 0.1 12087.21 (0.28%) 0.19 128 14810.33 0.04 14894.08 (0.57%) 0.08 Oracle DB on 2 socket, 44 core and 88 threads Intel x86 machine (normalized, higher is better): users baseline %stdev patch %stdev 20 1 0.9 1.0056 (0.56%) 0.34 40 1 0.8 1.0173 (1.73%) 0.13 60 1 0.34 0.9995 (-0.05%) 0.85 80 1 0.53 1.0175 (1.75%) 1.56 100 1 0.79 1.0151 (1.51%) 1.31 120 1 0.06 1.0244 (2.44%) 0.5 140 1 0.22 1.034 (3.4%) 0.66 160 1 0.57 1.0362 (3.62%) 0.07 180 1 0.81 1.041 (4.1%) 0.8 200 1 0.44 1.0233 (2.33%) 1.4 220 1 1.74 1.0125 (1.25%) 1.41 Uperf pingpong on 2 socket, 44 core and 88 threads Intel x86 machine with message size = 8k (higher is better): threads baseline %stdev patch %stdev 8 45.36 0.43 46.94 (3.48%) 0.2 16 87.81 0.82 91.75 (4.49%) 0.43 32 151.19 0.02 167.74 (10.95%) 1.29 48 190.2 0.21 200.57 (5.45%) 0.89 64 190.42 0.35 226.74 (19.07%) 1.79 128 323.86 0.28 348.12 (7.49%) 0.77 Dbench on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): clients baseline patch 1 629.8 600.19 (-4.7%) 2 1159.65 1162.07 (0.21%) 4 2121.61 2112.27 (-0.44%) 8 2620.52 2645.55 (0.96%) 16 2879.31 2828.87 (-1.75%) 32 2791.24 2760.97 (-1.08%) 64 1853.07 1747.66 (-5.69%) 128 1484.95 1459.81 (-1.69%) Tbench on 2 socket, 44 core and 88 threads Intel x86 machine (higher is better): clients baseline patch 1 256.41 258.11 (0.67%) 2 509.89 509.13 (-0.15%) 4 999.44 1016.58 (1.72%) 8 1982.7 2006.53 (1.2%) 16 3891.51 3964.43 (1.87%) 32 6819.24 7376.92 (8.18%) 64 8542.95 9660.45 (13.08%) 128 15277.6 15438.4 (1.05%) Schbench on 2 socket, 44 core and 88 threads Intel x86 machine with 44 tasks (lower is better): percentile baseline %stdev patch %stdev 50 94 2.82 94.67 (-0.71%) 2.2 75 124 2.13 124.67 (-0.54%) 1.67 90 152 1.74 154.33 (-1.54%) 0.75 95 171 2.11 176.67 (-3.31%) 0.86 99 512.67 104.96 4130.33 (-705.65%) 79.41 99.5 2296 82.55 10066.67 (-338.44%) 26.15 99.9 12517.33 2.38 12869.33 (-2.81%) 0.8 Hackbench process on 2 socket, 16 core and 128 threads SPARC machine (lower is better): groups baseline %stdev patch %stdev 1 1.3085 6.65 1.2514 (4.36%) 11.1 2 1.4559 8.55 1.5433 (-6%) 3.05 4 2.6271 1.74 2.5626 (2.5%) 2.69 8 4.7089 3.01 4.5316 (3.77%) 2.95 16 8.7406 2.25 8.6585 (0.94%) 2.91 32 17.7835 1.01 17.175 (3.42%) 1.38 64 36.1901 0.65 35.5294 (1.83%) 1.02 128 72.6585 0.51 71.8821 (1.07%) 1.05 Following are the schbench performance numbers with SIS_CORE false and SIS_PROP false. This recovers the latency increase by having SIS_CORE false. Schbench on 2 socket, 44 core and 88 threads Intel x86 machine with 44 tasks (lower is better): percentile baseline %stdev patch %stdev 50 94 2.82 93.33 (0.71%) 1.24 75 124 2.13 122.67 (1.08%) 1.7 90 152 1.74 149.33 (1.75%) 2.35 95 171 2.11 167 (2.34%) 2.74 99 512.67 104.96 206 (59.82%) 8.86 99.5 2296 82.55 3121.67 (-35.96%) 97.37 99.9 12517.33 2.38 12592 (-0.6%) 1.67 Changes from v2->v3: -Use shift operator instead of multiplication to compute limit -Use per-CPU variable to precompute the number of sibling SMTs for x86 subhra mazumdar (7): sched: limit cpu search in select_idle_cpu sched: introduce per-cpu var next_cpu to track search limit sched: rotate the cpu search window for better spread sched: add sched feature to disable idle core search sched: SIS_CORE to disable idle core search x86/smpboot: introduce per-cpu variable for HT siblings sched: use per-cpu variable cpumask_weight_sibling arch/x86/include/asm/smp.h | 1 + arch/x86/include/asm/topology.h | 1 + arch/x86/kernel/smpboot.c | 17 ++++++++++++++++- include/linux/topology.h | 4 ++++ kernel/sched/core.c | 2 ++ kernel/sched/fair.c | 31 +++++++++++++++++++++++-------- kernel/sched/features.h | 1 + kernel/sched/sched.h | 1 + 8 files changed, 49 insertions(+), 9 deletions(-) -- 2.9.3