From 14c73bd344da60abaf7da3ea2e7733ddda35bbac Mon Sep 17 00:00:00 2001 From: Srikar Dronamraju Date: Thu, 5 Dec 2019 14:02:17 +0530 Subject: [PATCH] powerpc/vcpu: Assume dedicated processors as non-preempt With commit 247f2f6f3c70 ("sched/core: Don't schedule threads on pre-empted vCPUs"), the scheduler avoids preempted vCPUs to schedule tasks on wakeup. This leads to wrong choice of CPU, which in-turn leads to larger wakeup latencies. Eventually, it leads to performance regression in latency sensitive benchmarks like soltp, schbench etc. On Powerpc, vcpu_is_preempted() only looks at yield_count. If the yield_count is odd, the vCPU is assumed to be preempted. However yield_count is increased whenever the LPAR enters CEDE state (idle). So any CPU that has entered CEDE state is assumed to be preempted. Even if vCPU of dedicated LPAR is preempted/donated, it should have right of first-use since they are supposed to own the vCPU. On a Power9 System with 32 cores: # lscpu Architecture: ppc64le Byte Order: Little Endian CPU(s): 128 On-line CPU(s) list: 0-127 Thread(s) per core: 8 Core(s) per socket: 1 Socket(s): 16 NUMA node(s): 2 Model: 2.2 (pvr 004e 0202) Model name: POWER9 (architected), altivec supported Hypervisor vendor: pHyp Virtualization type: para L1d cache: 32K L1i cache: 32K L2 cache: 512K L3 cache: 10240K NUMA node0 CPU(s): 0-63 NUMA node1 CPU(s): 64-127 # perf stat -a -r 5 ./schbench v5.4 v5.4 + patch Latency percentiles (usec) Latency percentiles (usec) 50.0000th: 45 50.0th: 45 75.0000th: 62 75.0th: 63 90.0000th: 71 90.0th: 74 95.0000th: 77 95.0th: 78 *99.0000th: 91 *99.0th: 82 99.5000th: 707 99.5th: 83 99.9000th: 6920 99.9th: 86 min=0, max=10048 min=0, max=96 Latency percentiles (usec) Latency percentiles (usec) 50.0000th: 45 50.0th: 46 75.0000th: 61 75.0th: 64 90.0000th: 72 90.0th: 75 95.0000th: 79 95.0th: 79 *99.0000th: 691 *99.0th: 83 99.5000th: 3972 99.5th: 85 99.9000th: 8368 99.9th: 91 min=0, max=16606 min=0, max=117 Latency percentiles (usec) Latency percentiles (usec) 50.0000th: 45 50.0th: 46 75.0000th: 61 75.0th: 64 90.0000th: 71 90.0th: 75 95.0000th: 77 95.0th: 79 *99.0000th: 106 *99.0th: 83 99.5000th: 2364 99.5th: 84 99.9000th: 7480 99.9th: 90 min=0, max=10001 min=0, max=95 Latency percentiles (usec) Latency percentiles (usec) 50.0000th: 45 50.0th: 47 75.0000th: 62 75.0th: 65 90.0000th: 72 90.0th: 75 95.0000th: 78 95.0th: 79 *99.0000th: 93 *99.0th: 84 99.5000th: 108 99.5th: 85 99.9000th: 6792 99.9th: 90 min=0, max=17681 min=0, max=117 Latency percentiles (usec) Latency percentiles (usec) 50.0000th: 46 50.0th: 45 75.0000th: 62 75.0th: 64 90.0000th: 73 90.0th: 75 95.0000th: 79 95.0th: 79 *99.0000th: 113 *99.0th: 82 99.5000th: 2724 99.5th: 83 99.9000th: 6184 99.9th: 93 min=0, max=9887 min=0, max=111 Performance counter stats for 'system wide' (5 runs): context-switches 43,373 ( +- 0.40% ) 44,597 ( +- 0.55% ) cpu-migrations 1,211 ( +- 5.04% ) 220 ( +- 6.23% ) page-faults 15,983 ( +- 5.21% ) 15,360 ( +- 3.38% ) Waiman Long suggested using static_keys. Fixes: 247f2f6f3c70 ("sched/core: Don't schedule threads on pre-empted vCPUs") Cc: stable@vger.kernel.org # v4.18+ Reported-by: Parth Shah Reported-by: Ihor Pasichnyk Tested-by: Juri Lelli Acked-by: Waiman Long Reviewed-by: Gautham R. Shenoy Signed-off-by: Srikar Dronamraju Acked-by: Phil Auld Reviewed-by: Vaidyanathan Srinivasan Tested-by: Parth Shah [mpe: Move the key and setting of the key to pseries/setup.c] Signed-off-by: Michael Ellerman Link: https://lore.kernel.org/r/20191213035036.6913-1-mpe@ellerman.id.au --- arch/powerpc/include/asm/spinlock.h | 4 +++- arch/powerpc/platforms/pseries/setup.c | 7 +++++++ 2 files changed, 10 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h index e9a960e28f3c8..cac95a3f30c26 100644 --- a/arch/powerpc/include/asm/spinlock.h +++ b/arch/powerpc/include/asm/spinlock.h @@ -36,10 +36,12 @@ #endif #ifdef CONFIG_PPC_PSERIES +DECLARE_STATIC_KEY_FALSE(shared_processor); + #define vcpu_is_preempted vcpu_is_preempted static inline bool vcpu_is_preempted(int cpu) { - if (!firmware_has_feature(FW_FEATURE_SPLPAR)) + if (!static_branch_unlikely(&shared_processor)) return false; return !!(be32_to_cpu(lppaca_of(cpu).yield_count) & 1); } diff --git a/arch/powerpc/platforms/pseries/setup.c b/arch/powerpc/platforms/pseries/setup.c index 0a40201f315ff..0c8421dd01ab5 100644 --- a/arch/powerpc/platforms/pseries/setup.c +++ b/arch/powerpc/platforms/pseries/setup.c @@ -74,6 +74,9 @@ #include "pseries.h" #include "../../../../drivers/pci/pci.h" +DEFINE_STATIC_KEY_FALSE(shared_processor); +EXPORT_SYMBOL_GPL(shared_processor); + int CMO_PrPSP = -1; int CMO_SecPSP = -1; unsigned long CMO_PageSize = (ASM_CONST(1) << IOMMU_PAGE_SHIFT_4K); @@ -758,6 +761,10 @@ static void __init pSeries_setup_arch(void) if (firmware_has_feature(FW_FEATURE_LPAR)) { vpa_init(boot_cpuid); + + if (lppaca_shared_proc(get_lppaca())) + static_branch_enable(&shared_processor); + ppc_md.power_save = pseries_lpar_idle; ppc_md.enable_pmcs = pseries_lpar_enable_pmcs; #ifdef CONFIG_PCI_IOV