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Commit c347a2f1 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
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perf/x86: Add a few more comments 



Add a few comments on the ->add(), ->del() and ->*_txn()
implementation.

Requested-by: default avatarVince Weaver <vincent.weaver@maine.edu>
Signed-off-by: default avatarPeter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-he3819318c245j7t5e1e22tr@git.kernel.org


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent fdded676

arch/x86/kernel/cpu/perf_event.c

+33 −14
Original line number Diff line number Diff line
@@ -892,7 +892,6 @@ static void x86_pmu_enable(struct pmu *pmu) 
		 * hw_perf_group_sched_in() or x86_pmu_enable()

		 *

		 * step1: save events moving to new counters

		 * step2: reprogram moved events into new counters

		 */

		for (i = 0; i < n_running; i++) {

			event = cpuc->event_list[i];
@@ -918,6 +917,9 @@ static void x86_pmu_enable(struct pmu *pmu) 
			x86_pmu_stop(event, PERF_EF_UPDATE);

		}



		/*

		 * step2: reprogram moved events into new counters

		 */

		for (i = 0; i < cpuc->n_events; i++) {

			event = cpuc->event_list[i];

			hwc = &event->hw;
@@ -1043,7 +1045,7 @@ static int x86_pmu_add(struct perf_event *event, int flags) 
	/*

	 * If group events scheduling transaction was started,

	 * skip the schedulability test here, it will be performed

	 * at commit time (->commit_txn) as a whole

	 * at commit time (->commit_txn) as a whole.

	 */

	if (cpuc->group_flag & PERF_EVENT_TXN)

		goto done_collect;
@@ -1058,6 +1060,10 @@ static int x86_pmu_add(struct perf_event *event, int flags) 
	memcpy(cpuc->assign, assign, n*sizeof(int));



done_collect:

	/*

	 * Commit the collect_events() state. See x86_pmu_del() and

	 * x86_pmu_*_txn().

	 */

	cpuc->n_events = n;

	cpuc->n_added += n - n0;

	cpuc->n_txn += n - n0;
@@ -1183,28 +1189,38 @@ static void x86_pmu_del(struct perf_event *event, int flags) 
	 * If we're called during a txn, we don't need to do anything.

	 * The events never got scheduled and ->cancel_txn will truncate

	 * the event_list.

	 *

	 * XXX assumes any ->del() called during a TXN will only be on

	 * an event added during that same TXN.

	 */

	if (cpuc->group_flag & PERF_EVENT_TXN)

		return;



	/*

	 * Not a TXN, therefore cleanup properly.

	 */

	x86_pmu_stop(event, PERF_EF_UPDATE);



	for (i = 0; i < cpuc->n_events; i++) {

		if (event == cpuc->event_list[i]) {

		if (event == cpuc->event_list[i])

			break;

	}



	if (WARN_ON_ONCE(i == cpuc->n_events)) /* called ->del() without ->add() ? */

		return;



	/* If we have a newly added event; make sure to decrease n_added. */

	if (i >= cpuc->n_events - cpuc->n_added)

		--cpuc->n_added;



	if (x86_pmu.put_event_constraints)

		x86_pmu.put_event_constraints(cpuc, event);



	/* Delete the array entry. */

	while (++i < cpuc->n_events)

		cpuc->event_list[i-1] = cpuc->event_list[i];



	--cpuc->n_events;

			break;

		}

	}



	perf_event_update_userpage(event);

}
@@ -1598,7 +1614,8 @@ static void x86_pmu_cancel_txn(struct pmu *pmu) 
{

	__this_cpu_and(cpu_hw_events.group_flag, ~PERF_EVENT_TXN);

	/*

	 * Truncate the collected events.

	 * Truncate collected array by the number of events added in this

	 * transaction. See x86_pmu_add() and x86_pmu_*_txn().

	 */

	__this_cpu_sub(cpu_hw_events.n_added, __this_cpu_read(cpu_hw_events.n_txn));

	__this_cpu_sub(cpu_hw_events.n_events, __this_cpu_read(cpu_hw_events.n_txn));
@@ -1609,6 +1626,8 @@ static void x86_pmu_cancel_txn(struct pmu *pmu) 
 * Commit group events scheduling transaction

 * Perform the group schedulability test as a whole

 * Return 0 if success

 *

 * Does not cancel the transaction on failure; expects the caller to do this.

 */

static int x86_pmu_commit_txn(struct pmu *pmu)

{

arch/x86/kernel/cpu/perf_event.h

+5 −3
Original line number Diff line number Diff line
@@ -130,9 +130,11 @@ struct cpu_hw_events { 
	unsigned long		running[BITS_TO_LONGS(X86_PMC_IDX_MAX)];

	int			enabled;



	int			n_events;

	int			n_added;

	int			n_txn;

	int			n_events; /* the # of events in the below arrays */

	int			n_added;  /* the # last events in the below arrays;

					     they've never been enabled yet */

	int			n_txn;    /* the # last events in the below arrays;

					     added in the current transaction */

	int			assign[X86_PMC_IDX_MAX]; /* event to counter assignment */

	u64			tags[X86_PMC_IDX_MAX];

	struct perf_event	*event_list[X86_PMC_IDX_MAX]; /* in enabled order */