From: Athira Rajeev atrajeev@linux.vnet.ibm.com
[ 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@ellerman.id.au Signed-off-by: Athira Rajeev atrajeev@linux.vnet.ibm.com [mpe: Reflow comment and if formatting] Signed-off-by: Michael Ellerman mpe@ellerman.id.au Link: https://lore.kernel.org/r/1612516492-1428-1-git-send-email-atrajeev@linux.vn... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/powerpc/perf/core-book3s.c | 19 +++++++++++++++---- 1 file changed, 15 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c index 70de13822828..091bdeaf02a3 100644 --- a/arch/powerpc/perf/core-book3s.c +++ b/arch/powerpc/perf/core-book3s.c @@ -2046,7 +2046,17 @@ 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) @@ -2064,9 +2074,10 @@ 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.