From: Peter Zijlstra <peterz@infradead.org>
To: Vince Weaver <vincent.weaver@maine.edu>
Cc: Dave Jones <davej@redhat.com>,
Linux Kernel <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>, Paul Mackerras <paulus@samba.org>,
Steven Rostedt <rostedt@goodmis.org>,
Stephane Eranian <eranian@google.com>
Subject: Re: x86_pmu_start WARN_ON.
Date: Mon, 24 Feb 2014 12:28:39 +0100 [thread overview]
Message-ID: <20140224112839.GQ15586@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <alpine.DEB.2.10.1402211514560.6395@vincent-weaver-1.um.maine.edu>
On Fri, Feb 21, 2014 at 03:18:38PM -0500, Vince Weaver wrote:
> I've applied the patch and have been unable to trigger the warning with
> either my testcase or a few hours of fuzzing.
Yay.
> My only comment on the patch is it could always use some comments.
>
> The perf_event code is really hard to follow as is, without adding
> more uncommented special cases.
Does the below help a bit? Or is there anywhere in particular you want
more comments?
---
Subject: perf, x86: Add a few more comments
From: Peter Zijlstra <peterz@infradead.org>
Date: Mon Feb 24 12:26:21 CET 2014
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>
---
arch/x86/kernel/cpu/perf_event.c | 49 +++++++++++++++++++++++++++------------
arch/x86/kernel/cpu/perf_event.h | 8 +++---
2 files changed, 39 insertions(+), 18 deletions(-)
--- 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 *p
* 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 *p
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
/*
* 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
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_even
* 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 (i >= cpuc->n_events - cpuc->n_added)
- --cpuc->n_added;
+ if (event == cpuc->event_list[i])
+ break;
+ }
- if (x86_pmu.put_event_constraints)
- x86_pmu.put_event_constraints(cpuc, event);
+ if (WARN_ON_ONCE(i == cpuc->n_events)) /* called ->del() without ->add() ? */
+ return;
- while (++i < cpuc->n_events)
- cpuc->event_list[i-1] = cpuc->event_list[i];
+ /* 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;
- --cpuc->n_events;
- break;
- }
- }
perf_event_update_userpage(event);
}
@@ -1598,7 +1614,8 @@ static void x86_pmu_cancel_txn(struct pm
{
__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 pm
* 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)
{
--- 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 */
next prev parent reply other threads:[~2014-02-24 11:28 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-30 19:02 x86_pmu_start WARN_ON Dave Jones
2014-02-10 21:26 ` Vince Weaver
2014-02-11 13:29 ` Peter Zijlstra
2014-02-12 21:04 ` Vince Weaver
2014-02-13 14:11 ` Vince Weaver
2014-02-13 17:35 ` Vince Weaver
2014-02-13 22:13 ` Vince Weaver
2014-02-17 15:28 ` Peter Zijlstra
2014-02-18 18:30 ` Vince Weaver
2014-02-18 22:20 ` Vince Weaver
2014-02-19 10:19 ` Peter Zijlstra
2014-02-19 22:34 ` Vince Weaver
2014-02-20 10:08 ` Peter Zijlstra
2014-02-20 15:47 ` Andi Kleen
2014-02-20 15:54 ` Peter Zijlstra
2014-02-20 17:31 ` Andi Kleen
2014-02-20 18:15 ` Peter Zijlstra
2014-02-20 18:23 ` Andi Kleen
2014-02-20 19:04 ` Steven Rostedt
2014-02-20 16:26 ` Steven Rostedt
2014-02-20 17:00 ` Peter Zijlstra
2014-02-20 17:43 ` Steven Rostedt
2014-02-20 17:46 ` Steven Rostedt
2014-02-20 18:18 ` Peter Zijlstra
2014-02-20 18:03 ` Vince Weaver
2014-02-20 18:23 ` Peter Zijlstra
2014-02-20 18:54 ` Vince Weaver
2014-02-20 19:21 ` Vince Weaver
2014-02-20 19:46 ` Vince Weaver
2014-02-21 14:37 ` Vince Weaver
2014-02-21 15:03 ` Peter Zijlstra
2014-02-21 20:18 ` Vince Weaver
2014-02-24 11:28 ` Peter Zijlstra [this message]
2014-02-26 5:59 ` Vince Weaver
2014-02-27 13:32 ` [tip:perf/core] perf/x86: Fix event scheduling tip-bot for Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20140224112839.GQ15586@twins.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=davej@redhat.com \
--cc=eranian@google.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@redhat.com \
--cc=paulus@samba.org \
--cc=rostedt@goodmis.org \
--cc=vincent.weaver@maine.edu \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).