lkml.org 
[lkml]   [2014]   [Feb]   [27]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[tip:perf/core] perf/x86: Add a few more comments
Commit-ID:  c347a2f1793e285b0812343e715bb7e953dbdf68
Gitweb: http://git.kernel.org/tip/c347a2f1793e285b0812343e715bb7e953dbdf68
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Mon, 24 Feb 2014 12:26:21 +0100
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Thu, 27 Feb 2014 12:43:25 +0100

perf/x86: Add a few more comments

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

Requested-by: Vince Weaver <vincent.weaver@maine.edu>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/n/tip-he3819318c245j7t5e1e22tr@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
arch/x86/kernel/cpu/perf_event.c | 47 ++++++++++++++++++++++++++++------------
arch/x86/kernel/cpu/perf_event.h | 8 ++++---
2 files changed, 38 insertions(+), 17 deletions(-)

diff --git a/arch/x86/kernel/cpu/perf_event.c b/arch/x86/kernel/cpu/perf_event.c
index 79f9f84..ae407f7 100644
--- a/arch/x86/kernel/cpu/perf_event.c
+++ b/arch/x86/kernel/cpu/perf_event.c
@@ -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 (i >= cpuc->n_events - cpuc->n_added)
- --cpuc->n_added;
+ if (WARN_ON_ONCE(i == cpuc->n_events)) /* called ->del() without ->add() ? */
+ return;

- if (x86_pmu.put_event_constraints)
- x86_pmu.put_event_constraints(cpuc, event);
+ /* If we have a newly added event; make sure to decrease n_added. */
+ if (i >= cpuc->n_events - cpuc->n_added)
+ --cpuc->n_added;

- while (++i < cpuc->n_events)
- cpuc->event_list[i-1] = cpuc->event_list[i];
+ 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;

- --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)
{
diff --git a/arch/x86/kernel/cpu/perf_event.h b/arch/x86/kernel/cpu/perf_event.h
index 4972c24..3b2f9bd 100644
--- a/arch/x86/kernel/cpu/perf_event.h
+++ b/arch/x86/kernel/cpu/perf_event.h
@@ -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 */

\
 
 \ /
  Last update: 2014-02-27 16:01    [W:0.035 / U:121.800 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site