* [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt
@ 2019-12-13 3:50 Michael Ellerman
2019-12-13 3:50 ` [PATCH v5 2/2] powerpc/shared: Use static key to detect shared processor Michael Ellerman
` (2 more replies)
0 siblings, 3 replies; 5+ messages in thread
From: Michael Ellerman @ 2019-12-13 3:50 UTC (permalink / raw)
To: linuxppc-dev
Cc: juri.lelli, parth, pauld, srikar, ego, Ihor.Pasichnyk, longman
From: Srikar Dronamraju <srikar@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@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>
---
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
^ permalink raw reply related [flat|nested] 5+ messages in thread
* [PATCH v5 2/2] powerpc/shared: Use static key to detect shared processor
2019-12-13 3:50 [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Michael Ellerman
@ 2019-12-13 3:50 ` Michael Ellerman
2019-12-13 5:07 ` [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Srikar Dronamraju
2019-12-13 21:19 ` Michael Ellerman
2 siblings, 0 replies; 5+ messages in thread
From: Michael Ellerman @ 2019-12-13 3:50 UTC (permalink / raw)
To: linuxppc-dev
Cc: juri.lelli, parth, pauld, srikar, ego, Ihor.Pasichnyk, longman
From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
With the static key shared processor available, is_shared_processor()
can return without having to query the lppaca structure.
Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Phil Auld <pauld@redhat.com>
Acked-by: Waiman Long <longman@redhat.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20191205083218.25824-2-srikar@linux.vnet.ibm.com
---
arch/powerpc/include/asm/spinlock.h | 9 ++-------
1 file changed, 2 insertions(+), 7 deletions(-)
v5: No change.
diff --git a/arch/powerpc/include/asm/spinlock.h b/arch/powerpc/include/asm/spinlock.h
index cac95a3f30c2..1b55fc08f853 100644
--- a/arch/powerpc/include/asm/spinlock.h
+++ b/arch/powerpc/include/asm/spinlock.h
@@ -112,13 +112,8 @@ static inline void splpar_rw_yield(arch_rwlock_t *lock) {};
static inline bool is_shared_processor(void)
{
-/*
- * LPPACA is only available on Pseries so guard anything LPPACA related to
- * allow other platforms (which include this common header) to compile.
- */
-#ifdef CONFIG_PPC_PSERIES
- return (IS_ENABLED(CONFIG_PPC_SPLPAR) &&
- lppaca_shared_proc(local_paca->lppaca_ptr));
+#ifdef CONFIG_PPC_SPLPAR
+ return static_branch_unlikely(&shared_processor);
#else
return false;
#endif
--
2.21.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt
2019-12-13 3:50 [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Michael Ellerman
2019-12-13 3:50 ` [PATCH v5 2/2] powerpc/shared: Use static key to detect shared processor Michael Ellerman
@ 2019-12-13 5:07 ` Srikar Dronamraju
2019-12-13 10:06 ` Michael Ellerman
2019-12-13 21:19 ` Michael Ellerman
2 siblings, 1 reply; 5+ messages in thread
From: Srikar Dronamraju @ 2019-12-13 5:07 UTC (permalink / raw)
To: Michael Ellerman
Cc: juri.lelli, ego, pauld, parth, Ihor.Pasichnyk, linuxppc-dev, longman
* Michael Ellerman <mpe@ellerman.id.au> [2019-12-13 14:50:35]:
> 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>
> ---
> arch/powerpc/include/asm/spinlock.h | 4 +++-
> arch/powerpc/platforms/pseries/setup.c | 7 +++++++
> 2 files changed, 10 insertions(+), 1 deletion(-)
>
Tested with your version of the patch and its working as expected
Latency percentiles (usec)
50.0th: 45
75.0th: 63
90.0th: 74
95.0th: 78
*99.0th: 82
99.5th: 83
99.9th: 86
min=0, max=96
Latency percentiles (usec)
50.0th: 46
75.0th: 64
90.0th: 75
95.0th: 79
*99.0th: 83
99.5th: 85
99.9th: 91
min=0, max=117
Latency percentiles (usec)
50.0th: 46
75.0th: 64
90.0th: 75
95.0th: 79
*99.0th: 83
99.5th: 84
99.9th: 90
min=0, max=95
Latency percentiles (usec)
50.0th: 47
75.0th: 65
90.0th: 75
95.0th: 79
*99.0th: 84
99.5th: 85
99.9th: 90
min=0, max=117
Latency percentiles (usec)
50.0th: 45
75.0th: 64
90.0th: 75
95.0th: 79
*99.0th: 82
99.5th: 83
99.9th: 93
min=0, max=111
--
Thanks and Regards
Srikar Dronamraju
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt
2019-12-13 5:07 ` [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Srikar Dronamraju
@ 2019-12-13 10:06 ` Michael Ellerman
0 siblings, 0 replies; 5+ messages in thread
From: Michael Ellerman @ 2019-12-13 10:06 UTC (permalink / raw)
To: Srikar Dronamraju
Cc: juri.lelli, ego, pauld, parth, Ihor.Pasichnyk, linuxppc-dev, longman
Srikar Dronamraju <srikar@linux.vnet.ibm.com> writes:
> * Michael Ellerman <mpe@ellerman.id.au> [2019-12-13 14:50:35]:
>
>> 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>
>> ---
>> arch/powerpc/include/asm/spinlock.h | 4 +++-
>> arch/powerpc/platforms/pseries/setup.c | 7 +++++++
>> 2 files changed, 10 insertions(+), 1 deletion(-)
>>
>
> Tested with your version of the patch and its working as expected
Thanks, I took the values below and put them in the changelog for the
patched case.
cheers
> Latency percentiles (usec)
> 50.0th: 45
> 75.0th: 63
> 90.0th: 74
> 95.0th: 78
> *99.0th: 82
> 99.5th: 83
> 99.9th: 86
> min=0, max=96
> Latency percentiles (usec)
> 50.0th: 46
> 75.0th: 64
> 90.0th: 75
> 95.0th: 79
> *99.0th: 83
> 99.5th: 85
> 99.9th: 91
> min=0, max=117
> Latency percentiles (usec)
> 50.0th: 46
> 75.0th: 64
> 90.0th: 75
> 95.0th: 79
> *99.0th: 83
> 99.5th: 84
> 99.9th: 90
> min=0, max=95
> Latency percentiles (usec)
> 50.0th: 47
> 75.0th: 65
> 90.0th: 75
> 95.0th: 79
> *99.0th: 84
> 99.5th: 85
> 99.9th: 90
> min=0, max=117
> Latency percentiles (usec)
> 50.0th: 45
> 75.0th: 64
> 90.0th: 75
> 95.0th: 79
> *99.0th: 82
> 99.5th: 83
> 99.9th: 93
> min=0, max=111
>
>
> --
> Thanks and Regards
> Srikar Dronamraju
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt
2019-12-13 3:50 [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Michael Ellerman
2019-12-13 3:50 ` [PATCH v5 2/2] powerpc/shared: Use static key to detect shared processor Michael Ellerman
2019-12-13 5:07 ` [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Srikar Dronamraju
@ 2019-12-13 21:19 ` Michael Ellerman
2 siblings, 0 replies; 5+ messages in thread
From: Michael Ellerman @ 2019-12-13 21:19 UTC (permalink / raw)
To: Michael Ellerman, linuxppc-dev
Cc: juri.lelli, parth, pauld, srikar, ego, Ihor.Pasichnyk, longman
On Fri, 2019-12-13 at 03:50:35 UTC, Michael Ellerman wrote:
> From: Srikar Dronamraju <srikar@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.
...
>
> 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>
Series applied to powerpc fixes.
https://git.kernel.org/powerpc/c/14c73bd344da60abaf7da3ea2e7733ddda35bbac
cheers
^ permalink raw reply [flat|nested] 5+ messages in thread
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2019-12-13 3:50 [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Michael Ellerman
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2019-12-13 5:07 ` [PATCH v5 1/2] powerpc/vcpu: Assume dedicated processors as non-preempt Srikar Dronamraju
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