[PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt
Michael Ellerman
mpe at ellerman.id.au
Fri Dec 13 14:50:35 AEDT 2019
From: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
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 50.0000th: 39
75.0000th: 62 75.0000th: 53
90.0000th: 71 90.0000th: 67
95.0000th: 77 95.0000th: 76
*99.0000th: 91 *99.0000th: 89
99.5000th: 707 99.5000th: 93
99.9000th: 6920 99.9000th: 118
min=0, max=10048 min=0, max=211
Latency percentiles (usec) Latency percentiles (usec)
50.0000th: 45 50.0000th: 34
75.0000th: 61 75.0000th: 45
90.0000th: 72 90.0000th: 53
95.0000th: 79 95.0000th: 56
*99.0000th: 691 *99.0000th: 61
99.5000th: 3972 99.5000th: 63
99.9000th: 8368 99.9000th: 78
min=0, max=16606 min=0, max=228
Latency percentiles (usec) Latency percentiles (usec)
50.0000th: 45 50.0000th: 34
75.0000th: 61 75.0000th: 45
90.0000th: 71 90.0000th: 53
95.0000th: 77 95.0000th: 57
*99.0000th: 106 *99.0000th: 63
99.5000th: 2364 99.5000th: 68
99.9000th: 7480 99.9000th: 100
min=0, max=10001 min=0, max=134
Latency percentiles (usec) Latency percentiles (usec)
50.0000th: 45 50.0000th: 34
75.0000th: 62 75.0000th: 46
90.0000th: 72 90.0000th: 53
95.0000th: 78 95.0000th: 56
*99.0000th: 93 *99.0000th: 61
99.5000th: 108 99.5000th: 64
99.9000th: 6792 99.9000th: 85
min=0, max=17681 min=0, max=121
Latency percentiles (usec) Latency percentiles (usec)
50.0000th: 46 50.0000th: 33
75.0000th: 62 75.0000th: 44
90.0000th: 73 90.0000th: 51
95.0000th: 79 95.0000th: 54
*99.0000th: 113 *99.0000th: 61
99.5000th: 2724 99.5000th: 64
99.9000th: 6184 99.9000th: 82
min=0, max=9887 min=0, max=121
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 at vger.kernel.org # v4.18+
Reported-by: Parth Shah <parth at linux.ibm.com>
Reported-by: Ihor Pasichnyk <Ihor.Pasichnyk at ibm.com>
Tested-by: Juri Lelli <juri.lelli at redhat.com>
Acked-by: Waiman Long <longman at redhat.com>
Reviewed-by: Gautham R. Shenoy <ego at linux.vnet.ibm.com>
Signed-off-by: Srikar Dronamraju <srikar at linux.vnet.ibm.com>
Acked-by: Phil Auld <pauld at redhat.com>
Reviewed-by: Vaidyanathan Srinivasan <svaidy at linux.ibm.com>
Tested-by: Parth Shah <parth at linux.ibm.com>
[mpe: Move the key and setting of the key to pseries/setup.c]
Signed-off-by: Michael Ellerman <mpe at ellerman.id.au>
---
arch/powerpc/include/asm/spinlock.h | 4 +++-
arch/powerpc/platforms/pseries/setup.c | 7 +++++++
2 files changed, 10 insertions(+), 1 deletion(-)
v5: mpe: Move the key and setting of the key to pseries/setup.c
Changelog v1 (https://patchwork.ozlabs.org/patch/1204190/) ->v3:
Code is now under CONFIG_PPC_SPLPAR as it depends on CONFIG_PPC_PSERIES.
This was suggested by Waiman Long.
Changelog v3 (https://patchwork.ozlabs.org/patch/1204526) ->v4:
Fix a build issue in CONFIG_NUMA=n reported by Michael Ellerman
by moving the relevant code from mm/numa.c to kernel/smp.c
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index e9a960e28f3c..cac95a3f30c2 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 0a40201f315f..0c8421dd01ab 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
--
2.21.0
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