| From f2a4e31589a8540901da43ffd8ae1e92f3e39e8f Mon Sep 17 00:00:00 2001 |
| From: Srikar Dronamraju <srikar@linux.vnet.ibm.com> |
| Date: Thu, 5 Dec 2019 14:02:17 +0530 |
| Subject: [PATCH] powerpc/vcpu: Assume dedicated processors as non-preempt |
| |
| commit 14c73bd344da60abaf7da3ea2e7733ddda35bbac upstream. |
| |
| 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 <parth@linux.ibm.com> |
| Reported-by: Ihor Pasichnyk <Ihor.Pasichnyk@ibm.com> |
| Tested-by: Juri Lelli <juri.lelli@redhat.com> |
| Acked-by: Waiman Long <longman@redhat.com> |
| Reviewed-by: Gautham R. Shenoy <ego@linux.vnet.ibm.com> |
| Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com> |
| Acked-by: Phil Auld <pauld@redhat.com> |
| Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.ibm.com> |
| Tested-by: Parth Shah <parth@linux.ibm.com> |
| [mpe: Move the key and setting of the key to pseries/setup.c] |
| Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> |
| Link: https://lore.kernel.org/r/20191213035036.6913-1-mpe@ellerman.id.au |
| Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h |
| index a47f827bc5f1..897f26f45b4f 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 cc682759feae..c0a87b1cee24 100644 |
| --- a/arch/powerpc/platforms/pseries/setup.c |
| +++ b/arch/powerpc/platforms/pseries/setup.c |
| @@ -71,6 +71,9 @@ |
| #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); |
| @@ -780,6 +783,10 @@ 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 |
| -- |
| 2.7.4 |
| |
