Commit 2c2a9bbe authored Feb 12, 2018 by Kan Liang Committed by Ingo Molnar Mar 20, 2018

perf/x86/intel: Disable userspace RDPMC usage for large PEBS



Userspace RDPMC cannot possibly work for large PEBS, which was introduced in:

  b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt handling (large PEBS interrupt threshold)")

When the PEBS interrupt threshold is larger than one, there is no way
to get exact auto-reload times and value for userspace RDPMC.  Disable
the userspace RDPMC usage when large PEBS is enabled.

The only exception is when the PEBS interrupt threshold is 1, in which
case user-space RDPMC works well even with auto-reload events.

Signed-off-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
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: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Cc: acme@kernel.org
Fixes: b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt handling (large PEBS interrupt threshold)")
Link: http://lkml.kernel.org/r/1518474035-21006-6-git-send-email-kan.liang@linux.intel.com


Signed-off-by: Ingo Molnar <mingo@kernel.org>
(cherry picked from commit 1af22eba)

parent c698ca52

arch/x86/events/core.c

+2 −1

Original line number	Diff line number	Diff line
		@@ -2118,7 +2118,8 @@ static int x86_pmu_event_init(struct perf_event *event)
		event->destroy(event);
		}

		if (READ_ONCE(x86_pmu.attr_rdpmc))
		if (READ_ONCE(x86_pmu.attr_rdpmc) &&
		!(event->hw.flags & PERF_X86_EVENT_FREERUNNING))
		event->hw.flags \|= PERF_X86_EVENT_RDPMC_ALLOWED;

		return err;

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