This is a note to let you know that I've just added the patch titled
powerpc/perf: Record counter overflow always if SAMPLE_IP is unset
to the 4.14-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-perf-record-counter-overflow-always-if-sampl.patch
and it can be found in the queue-4.14 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit b9590c938ba8b3ff9fcf196a7994000faefcd6f4
Author: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
Date: Fri Feb 5 04:14:52 2021 -0500
powerpc/perf: Record counter overflow always if SAMPLE_IP is unset
[ Upstream commit d137845c973147a22622cc76c7b0bc16f6206323 ]
While sampling for marked events, currently we record the sample only
if the SIAR valid bit of Sampled Instruction Event Register (SIER) is
set. SIAR_VALID bit is used for fetching the instruction address from
Sampled Instruction Address Register(SIAR). But there are some
usecases, where the user is interested only in the PMU stats at each
counter overflow and the exact IP of the overflow event is not
required. Dropping SIAR invalid samples will fail to record some of
the counter overflows in such cases.
Example of such usecase is dumping the PMU stats (event counts) after
some regular amount of instructions/events from the userspace (ex: via
ptrace). Here counter overflow is indicated to userspace via signal
handler, and captured by monitoring and enabling I/O signaling on the
event file descriptor. In these cases, we expect to get
sample/overflow indication after each specified sample_period.
Perf event attribute will not have PERF_SAMPLE_IP set in the
sample_type if exact IP of the overflow event is not requested. So
while profiling if SAMPLE_IP is not set, just record the counter
overflow irrespective of SIAR_VALID check.
Suggested-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Athira Rajeev <atrajeev@xxxxxxxxxxxxxxxxxx>
[mpe: Reflow comment and if formatting]
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Link: https://lore.kernel.org/r/1612516492-1428-1-git-send-email-atrajeev@xxxxxxxxxxxxxxxxxx
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
index 56f16c803590..2669847434b8 100644
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -2055,7 +2055,17 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
left += period;
if (left <= 0)
left = period;
- record = siar_valid(regs);
+
+ /*
+ * If address is not requested in the sample via
+ * PERF_SAMPLE_IP, just record that sample irrespective
+ * of SIAR valid check.
+ */
+ if (event->attr.sample_type & PERF_SAMPLE_IP)
+ record = siar_valid(regs);
+ else
+ record = 1;
+
event->hw.last_period = event->hw.sample_period;
}
if (left < 0x80000000LL)
@@ -2073,9 +2083,10 @@ static void record_and_restart(struct perf_event *event, unsigned long val,
* MMCR2. Check attr.exclude_kernel and address to drop the sample in
* these cases.
*/
- if (event->attr.exclude_kernel && record)
- if (is_kernel_addr(mfspr(SPRN_SIAR)))
- record = 0;
+ if (event->attr.exclude_kernel &&
+ (event->attr.sample_type & PERF_SAMPLE_IP) &&
+ is_kernel_addr(mfspr(SPRN_SIAR)))
+ record = 0;
/*
* Finally record data if requested.
