linux-kernel - [PATCH V4 5/5] perf/x86: Fix: disable userspace RDPMC usage for large PEBS

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Message-Id: <1518474035-21006-6-git-send-email-kan.liang@linux.intel.com>
Date:   Mon, 12 Feb 2018 14:20:35 -0800
From:   kan.liang@...ux.intel.com
To:     peterz@...radead.org, mingo@...hat.com,
        linux-kernel@...r.kernel.org
Cc:     acme@...nel.org, tglx@...utronix.de, jolsa@...hat.com,
        eranian@...gle.com, ak@...ux.intel.com,
        Kan Liang <kan.liang@...ux.intel.com>
Subject: [PATCH V4 5/5] perf/x86: Fix: disable userspace RDPMC usage for large PEBS

From: Kan Liang <kan.liang@...ux.intel.com>

The userspace RDPMC usage never works for large PEBS since the large
PEBS is introduced by
commit 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.

For the PEBS interrupt threshold equals to one, even it's auto-reload
event, it doesn't need to disable the userspace RDPMC. It works well.

Fixes: b8241d20699e ("perf/x86/intel: Implement batched PEBS interrupt
handling (large PEBS interrupt threshold)")
Signed-off-by: Kan Liang <kan.liang@...ux.intel.com>
---
 arch/x86/events/core.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index 00a6251..9c86e10 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -2117,7 +2117,8 @@ 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;
-- 
2.7.4