Commit e758a33d authored May 12, 2009 by Paul Mackerras Committed by Ingo Molnar May 12, 2009

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@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <18953.25733.53359.147452@cargo.ozlabs.ibm.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 615a3f1e

kernel/perf_counter.c

+12 −7

Original line number	Diff line number	Diff line
		@@ -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)
		} 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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