linux-kernel - [PATCH] perf, x86: Fix :pp without LBR

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Date:	Thu,  7 Aug 2014 17:08:54 -0700
From:	Andi Kleen <andi@...stfloor.org>
To:	peterz@...radead.org
Cc:	kan.liang@...el.com, linux-kernel@...r.kernel.org,
	Andi Kleen <ak@...ux.intel.com>
Subject: [PATCH] perf, x86: Fix :pp without LBR

From: Andi Kleen <ak@...ux.intel.com>

This fixes a side effect of Kan's earlier patch to probe the LBRs at boot
time. Normally when the LBRs are disabled cycles:pp is disabled too.
So for example cycles:pp doesn't work.

However this is not needed with PEBSv2 and later (Haswell) because
it does not need LBRs to correct the IP-off-by-one.

So add an extra check for PEBSv2 that also allows :pp

Signed-off-by: Andi Kleen <ak@...ux.intel.com>
---
 arch/x86/kernel/cpu/perf_event.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 2879ecd..0646d3b 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -387,7 +387,7 @@ int x86_pmu_hw_config(struct perf_event *event)
 			precise++;
 
 			/* Support for IP fixup */
-			if (x86_pmu.lbr_nr)
+			if (x86_pmu.lbr_nr || x86_pmu.intel_cap.pebs_format >= 2)
 				precise++;
 		}
 
-- 
1.9.3

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