From: Stephane Eranian eranian@google.com
[ Upstream commit 583feb08e7f7ac9d533b446882eb3a54737a6dbb ]
When an event is programmed with attr.wakeup_events=N (N>0), it means the caller is interested in getting a user level notification after N samples have been recorded in the kernel sampling buffer.
With precise events on Intel processors, the kernel uses PEBS. The kernel tries minimize sampling overhead by verifying if the event configuration is compatible with multi-entry PEBS mode. If so, the kernel is notified only when the buffer has reached its threshold. Other PEBS operates in single-entry mode, the kenrel is notified for each PEBS sample.
The problem is that the current implementation look at frequency mode and event sample_type but ignores the wakeup_events field. Thus, it may not be possible to receive a notification after each precise event.
This patch fixes this problem by disabling multi-entry PEBS if wakeup_events is non-zero.
Signed-off-by: Stephane Eranian eranian@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Andi Kleen ak@linux.intel.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: Peter Zijlstra peterz@infradead.org Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Cc: kan.liang@intel.com Link: https://lkml.kernel.org/r/20190306195048.189514-1-eranian@google.com Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/kernel/cpu/perf_event_intel.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/arch/x86/kernel/cpu/perf_event_intel.c b/arch/x86/kernel/cpu/perf_event_intel.c index 7b79c80ce029..325ed90511cf 100644 --- a/arch/x86/kernel/cpu/perf_event_intel.c +++ b/arch/x86/kernel/cpu/perf_event_intel.c @@ -2513,7 +2513,7 @@ static int intel_pmu_hw_config(struct perf_event *event) return ret;
if (event->attr.precise_ip) { - if (!event->attr.freq) { + if (!(event->attr.freq || event->attr.wakeup_events)) { event->hw.flags |= PERF_X86_EVENT_AUTO_RELOAD; if (!(event->attr.sample_type & ~intel_pmu_free_running_flags(event)))