This is a note to let you know that I've just added the patch titled

perf/core: Fix ctx_event_type in ctx_resched()

to the 4.15-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...

The filename of the patch is: perf-core-fix-ctx_event_type-in-ctx_resched.patch and it can be found in the queue-4.15 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.

From bd903afeb504db5655a45bb4cf86f38be5b1bf62 Mon Sep 17 00:00:00 2001

From: Song Liu songliubraving@fb.com Date: Mon, 5 Mar 2018 21:55:04 -0800 Subject: perf/core: Fix ctx_event_type in ctx_resched()

From: Song Liu songliubraving@fb.com

commit bd903afeb504db5655a45bb4cf86f38be5b1bf62 upstream.

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 Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org

--- kernel/events/core.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

--- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -2246,7 +2246,7 @@ static void ctx_resched(struct perf_cpu_ 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_ 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);

Patches currently in stable-queue which might be from songliubraving@fb.com are

queue-4.15/perf-core-fix-ctx_event_type-in-ctx_resched.patch