linux-kernel - [tip:perfcounters/core] perf_counter: call hw_perf_save_disable/restore around group_sched

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Date:	Tue, 12 May 2009 13:33:31 GMT
From:	tip-bot for Paul Mackerras <paulus@...ba.org>
To:	linux-tip-commits@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, paulus@...ba.org, hpa@...or.com,
	mingo@...hat.com, a.p.zijlstra@...llo.nl, tglx@...utronix.de,
	cjashfor@...ux.vnet.ibm.com, mingo@...e.hu
Subject: [tip:perfcounters/core] perf_counter: call hw_perf_save_disable/restore around group_sched_in

Commit-ID:  e758a33d6fc5b9d6a3ae489863d04fcecad8120b
Gitweb:     http://git.kernel.org/tip/e758a33d6fc5b9d6a3ae489863d04fcecad8120b
Author:     Paul Mackerras <paulus@...ba.org>
AuthorDate: Tue, 12 May 2009 21:59:01 +1000
Committer:  Ingo Molnar <mingo@...e.hu>
CommitDate: Tue, 12 May 2009 15:31:06 +0200

perf_counter: call hw_perf_save_disable/restore around group_sched_in

I noticed that when enabling a group via the PERF_COUNTER_IOC_ENABLE
ioctl on the group leader, the counters weren't enabled and counting
immediately on return from the ioctl, but did start counting a little
while later (presumably after a context switch).

The reason was that __perf_counter_enable calls group_sched_in which
calls hw_perf_group_sched_in, which on powerpc assumes that the caller
has called hw_perf_save_disable already.  Until commit 46d686c6
("perf_counter: put whole group on when enabling group leader") it was
true that all callers of group_sched_in had called
hw_perf_save_disable first, and the powerpc hw_perf_group_sched_in
relies on that (there isn't an x86 version).

This fixes the problem by putting calls to hw_perf_save_disable /
hw_perf_restore around the calls to group_sched_in and
counter_sched_in in __perf_counter_enable.  Having the calls to
hw_perf_save_disable/restore around the counter_sched_in call is
harmless and makes this call consistent with the other call sites
of counter_sched_in, which have all called hw_perf_save_disable first.

[ Impact: more precise counter group disable/enable functionality ]

Signed-off-by: Paul Mackerras <paulus@...ba.org>
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc: Corey Ashford <cjashfor@...ux.vnet.ibm.com>
LKML-Reference: <18953.25733.53359.147452@...go.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>


---
 kernel/perf_counter.c |   19 ++++++++++++-------
 1 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 5ea0240..ff166c1 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -663,6 +663,7 @@ static void __perf_counter_enable(void *info)
 	struct perf_cpu_context *cpuctx = &__get_cpu_var(perf_cpu_context);
 	struct perf_counter_context *ctx = counter->ctx;
 	struct perf_counter *leader = counter->group_leader;
+	unsigned long pmuflags;
 	unsigned long flags;
 	int err;
 
@@ -689,14 +690,18 @@ static void __perf_counter_enable(void *info)
 	if (leader != counter && leader->state != PERF_COUNTER_STATE_ACTIVE)
 		goto unlock;
 
-	if (!group_can_go_on(counter, cpuctx, 1))
+	if (!group_can_go_on(counter, cpuctx, 1)) {
 		err = -EEXIST;
-	else if (counter == leader)
-		err = group_sched_in(counter, cpuctx, ctx,
-				     smp_processor_id());
-	else
-		err = counter_sched_in(counter, cpuctx, ctx,
-				       smp_processor_id());
+	} else {
+		pmuflags = hw_perf_save_disable();
+		if (counter == leader)
+			err = group_sched_in(counter, cpuctx, ctx,
+					     smp_processor_id());
+		else
+			err = counter_sched_in(counter, cpuctx, ctx,
+					       smp_processor_id());
+		hw_perf_restore(pmuflags);
+	}
 
 	if (err) {
 		/*
--
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