linux-kernel - [tip:perf/core] perf/x86-ibs: Fix frequency profiling

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Message-ID: <tip-6accb9cf76080422d400a641d9068b6b2a2c216f@git.kernel.org>
Date:	Wed, 9 May 2012 07:32:24 -0700
From:	tip-bot for Robert Richter <robert.richter@....com>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
	robert.richter@....com, a.p.zijlstra@...llo.nl, tglx@...utronix.de
Subject: [tip:perf/core] perf/x86-ibs: Fix frequency profiling

Commit-ID:  6accb9cf76080422d400a641d9068b6b2a2c216f
Gitweb:     http://git.kernel.org/tip/6accb9cf76080422d400a641d9068b6b2a2c216f
Author:     Robert Richter <robert.richter@....com>
AuthorDate: Mon, 2 Apr 2012 20:19:10 +0200
Committer:  Ingo Molnar <mingo@...nel.org>
CommitDate: Wed, 9 May 2012 15:23:13 +0200

perf/x86-ibs: Fix frequency profiling

Fixing profiling at a fixed frequency, in this case the freq value and
sample period was setup incorrectly. Since sampling periods are
adjusted we also allow periods that have lower 4 bits set.

Another fix is the setup of the hw counter: If we modify
hwc->sample_period, we also need to update hwc->last_period and
hwc->period_left.

Signed-off-by: Robert Richter <robert.richter@....com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Link: http://lkml.kernel.org/r/1333390758-10893-5-git-send-email-robert.richter@amd.com
Signed-off-by: Ingo Molnar <mingo@...nel.org>
---
 arch/x86/kernel/cpu/perf_event_amd_ibs.c |   18 ++++++++++++++++--
 1 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event_amd_ibs.c b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
index ebf169f..bc401bd 100644
--- a/arch/x86/kernel/cpu/perf_event_amd_ibs.c
+++ b/arch/x86/kernel/cpu/perf_event_amd_ibs.c
@@ -162,9 +162,16 @@ static int perf_ibs_init(struct perf_event *event)
 		if (config & perf_ibs->cnt_mask)
 			/* raw max_cnt may not be set */
 			return -EINVAL;
-		if (hwc->sample_period & 0x0f)
-			/* lower 4 bits can not be set in ibs max cnt */
+		if (!event->attr.sample_freq && hwc->sample_period & 0x0f)
+			/*
+			 * lower 4 bits can not be set in ibs max cnt,
+			 * but allowing it in case we adjust the
+			 * sample period to set a frequency.
+			 */
 			return -EINVAL;
+		hwc->sample_period &= ~0x0FULL;
+		if (!hwc->sample_period)
+			hwc->sample_period = 0x10;
 	} else {
 		max_cnt = config & perf_ibs->cnt_mask;
 		config &= ~perf_ibs->cnt_mask;
@@ -175,6 +182,13 @@ static int perf_ibs_init(struct perf_event *event)
 	if (!hwc->sample_period)
 		return -EINVAL;
 
+	/*
+	 * If we modify hwc->sample_period, we also need to update
+	 * hwc->last_period and hwc->period_left.
+	 */
+	hwc->last_period = hwc->sample_period;
+	local64_set(&hwc->period_left, hwc->sample_period);
+
 	hwc->config_base = perf_ibs->msr;
 	hwc->config = config;
 
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