* [PATCH] perf: correct ctx_event_type in ctx_resched()
@ 2018-03-06 5:55 Song Liu
2018-03-06 8:54 ` Peter Zijlstra
2018-03-09 9:07 ` [tip:perf/urgent] perf/core: Fix " tip-bot for Song Liu
0 siblings, 2 replies; 3+ messages in thread
From: Song Liu @ 2018-03-06 5:55 UTC (permalink / raw)
To: linux-kernel, peterz, jolsa; +Cc: kernel-team, ephiepark, Song Liu
In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
added. However, ctx_resched() calculates ctx_event_type before checking
this condition. As a result, pinned events will NOT get higher priority
than flexible events.
The following shows this issue on an Intel CPU (where ref-cycles can
only use one hardware counter).
1. First start:
perf stat -C 0 -e ref-cycles -I 1000
2. Then, in the second console, run:
perf stat -C 0 -e ref-cycles:D -I 1000
The second perf uses pinned events, which is expected to have higher
priority. However, because it failed in ctx_resched(). It is never
run.
This patch fixes this by calculating ctx_event_type after re-evaluating
event_type.
Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
Signed-off-by: Song Liu <songliubraving@fb.com>
Reported-by: Ephraim Park <ephiepark@fb.com>
---
kernel/events/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 5789810..cf52fc0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2246,7 +2246,7 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
struct perf_event_context *task_ctx,
enum event_type_t event_type)
{
- enum event_type_t ctx_event_type = event_type & EVENT_ALL;
+ enum event_type_t ctx_event_type;
bool cpu_event = !!(event_type & EVENT_CPU);
/*
@@ -2256,6 +2256,8 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
if (event_type & EVENT_PINNED)
event_type |= EVENT_FLEXIBLE;
+ ctx_event_type = event_type & EVENT_ALL;
+
perf_pmu_disable(cpuctx->ctx.pmu);
if (task_ctx)
task_ctx_sched_out(cpuctx, task_ctx, event_type);
--
2.9.5
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] perf: correct ctx_event_type in ctx_resched()
2018-03-06 5:55 [PATCH] perf: correct ctx_event_type in ctx_resched() Song Liu
@ 2018-03-06 8:54 ` Peter Zijlstra
2018-03-09 9:07 ` [tip:perf/urgent] perf/core: Fix " tip-bot for Song Liu
1 sibling, 0 replies; 3+ messages in thread
From: Peter Zijlstra @ 2018-03-06 8:54 UTC (permalink / raw)
To: Song Liu; +Cc: linux-kernel, jolsa, kernel-team, ephiepark
On Mon, Mar 05, 2018 at 09:55:04PM -0800, Song Liu wrote:
> In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
> added. However, ctx_resched() calculates ctx_event_type before checking
> this condition. As a result, pinned events will NOT get higher priority
> than flexible events.
>
> The following shows this issue on an Intel CPU (where ref-cycles can
> only use one hardware counter).
>
> 1. First start:
> perf stat -C 0 -e ref-cycles -I 1000
> 2. Then, in the second console, run:
> perf stat -C 0 -e ref-cycles:D -I 1000
>
> The second perf uses pinned events, which is expected to have higher
> priority. However, because it failed in ctx_resched(). It is never
> run.
>
> This patch fixes this by calculating ctx_event_type after re-evaluating
> event_type.
>
> Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
> Signed-off-by: Song Liu <songliubraving@fb.com>
> Reported-by: Ephraim Park <ephiepark@fb.com>
Thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread* [tip:perf/urgent] perf/core: Fix ctx_event_type in ctx_resched()
2018-03-06 5:55 [PATCH] perf: correct ctx_event_type in ctx_resched() Song Liu
2018-03-06 8:54 ` Peter Zijlstra
@ 2018-03-09 9:07 ` tip-bot for Song Liu
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot for Song Liu @ 2018-03-09 9:07 UTC (permalink / raw)
To: linux-tip-commits
Cc: mingo, tglx, torvalds, linux-kernel, hpa, ephiepark,
vincent.weaver, songliubraving, alexander.shishkin, peterz,
kernel-team, jolsa, acme, eranian
Commit-ID: bd903afeb504db5655a45bb4cf86f38be5b1bf62
Gitweb: https://git.kernel.org/tip/bd903afeb504db5655a45bb4cf86f38be5b1bf62
Author: Song Liu <songliubraving@fb.com>
AuthorDate: Mon, 5 Mar 2018 21:55:04 -0800
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Fri, 9 Mar 2018 08:03:02 +0100
perf/core: Fix ctx_event_type in ctx_resched()
In ctx_resched(), EVENT_FLEXIBLE should be sched_out when EVENT_PINNED is
added. However, ctx_resched() calculates ctx_event_type before checking
this condition. As a result, pinned events will NOT get higher priority
than flexible events.
The following shows this issue on an Intel CPU (where ref-cycles can
only use one hardware counter).
1. First start:
perf stat -C 0 -e ref-cycles -I 1000
2. Then, in the second console, run:
perf stat -C 0 -e ref-cycles:D -I 1000
The second perf uses pinned events, which is expected to have higher
priority. However, because it failed in ctx_resched(). It is never
run.
This patch fixes this by calculating ctx_event_type after re-evaluating
event_type.
Reported-by: Ephraim Park <ephiepark@fb.com>
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: <jolsa@redhat.com>
Cc: <kernel-team@fb.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Fixes: 487f05e18aa4 ("perf/core: Optimize event rescheduling on active contexts")
Link: http://lkml.kernel.org/r/20180306055504.3283731-1-songliubraving@fb.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
kernel/events/core.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 96db9ae5d5af..4b838470fac4 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2246,7 +2246,7 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
struct perf_event_context *task_ctx,
enum event_type_t event_type)
{
- enum event_type_t ctx_event_type = event_type & EVENT_ALL;
+ enum event_type_t ctx_event_type;
bool cpu_event = !!(event_type & EVENT_CPU);
/*
@@ -2256,6 +2256,8 @@ static void ctx_resched(struct perf_cpu_context *cpuctx,
if (event_type & EVENT_PINNED)
event_type |= EVENT_FLEXIBLE;
+ ctx_event_type = event_type & EVENT_ALL;
+
perf_pmu_disable(cpuctx->ctx.pmu);
if (task_ctx)
task_ctx_sched_out(cpuctx, task_ctx, event_type);
^ permalink raw reply related [flat|nested] 3+ messages in thread
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2018-03-06 5:55 [PATCH] perf: correct ctx_event_type in ctx_resched() Song Liu
2018-03-06 8:54 ` Peter Zijlstra
2018-03-09 9:07 ` [tip:perf/urgent] perf/core: Fix " tip-bot for Song Liu
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