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Date: Tue, 25 May 2010 17:58:06 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Stephane Eranian <eranian@...gle.com>
Cc: eranian@...il.com, linux-kernel@...r.kernel.org, mingo@...e.hu,
paulus@...ba.org, davem@...emloft.net, fweisbec@...il.com,
acme@...radead.org, ming.m.lin@...el.com,
perfmon2-devel@...ts.sf.net
Subject: Re: [PATCH] perf_events: fix event scheduling issues introduced by
transactional API (take 2)
On Tue, 2010-05-25 at 17:32 +0200, Peter Zijlstra wrote:
> > Because you always call cancel_txn() even when commit()
> > succeeds. I don't really understand why. I think it could be
> > avoided by clearing the group_flag in commit_txn() if it
> > succeeds. It would also make the logical flow more natural. Why
> > cancel something that has succeeded. You cancel when you fail/abort.
>
> Gah, I forgot about that. I think I suggested to Lin to do that and
> then
> promptly forgot.
>
> Let me add that and at least push this patch fwd, we can try and clean
> up that detail later on.
How about something like the below?
---
Subject: perf: Cleanup {start,commit,cancel}_txn details
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
Date: Tue May 25 17:49:05 CEST 2010
Clarify some of the transactional group scheduling API details
and change it so that a successfull ->commit_txn also closes
the transaction.
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <new-submission>
---
arch/powerpc/kernel/perf_event.c | 7 ++++---
arch/sparc/kernel/perf_event.c | 7 ++++---
arch/x86/kernel/cpu/perf_event.c | 14 +++++---------
include/linux/perf_event.h | 27 ++++++++++++++++++++++-----
kernel/perf_event.c | 8 +-------
5 files changed, 36 insertions(+), 27 deletions(-)
Index: linux-2.6/arch/powerpc/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/arch/powerpc/kernel/perf_event.c
+++ linux-2.6/arch/powerpc/kernel/perf_event.c
@@ -754,7 +754,7 @@ static int power_pmu_enable(struct perf_
* skip the schedulability test here, it will be peformed
* at commit time(->commit_txn) as a whole
*/
- if (cpuhw->group_flag & PERF_EVENT_TXN_STARTED)
+ if (cpuhw->group_flag & PERF_EVENT_TXN)
goto nocheck;
if (check_excludes(cpuhw->event, cpuhw->flags, n0, 1))
@@ -858,7 +858,7 @@ void power_pmu_start_txn(const struct pm
{
struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
- cpuhw->group_flag |= PERF_EVENT_TXN_STARTED;
+ cpuhw->group_flag |= PERF_EVENT_TXN;
cpuhw->n_txn_start = cpuhw->n_events;
}
@@ -871,7 +871,7 @@ void power_pmu_cancel_txn(const struct p
{
struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
- cpuhw->group_flag &= ~PERF_EVENT_TXN_STARTED;
+ cpuhw->group_flag &= ~PERF_EVENT_TXN;
}
/*
@@ -897,6 +897,7 @@ int power_pmu_commit_txn(const struct pm
for (i = cpuhw->n_txn_start; i < n; ++i)
cpuhw->event[i]->hw.config = cpuhw->events[i];
+ cpuhw->group_flag &= ~PERF_EVENT_TXN;
return 0;
}
Index: linux-2.6/arch/sparc/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/arch/sparc/kernel/perf_event.c
+++ linux-2.6/arch/sparc/kernel/perf_event.c
@@ -1005,7 +1005,7 @@ static int sparc_pmu_enable(struct perf_
* skip the schedulability test here, it will be peformed
* at commit time(->commit_txn) as a whole
*/
- if (cpuc->group_flag & PERF_EVENT_TXN_STARTED)
+ if (cpuc->group_flag & PERF_EVENT_TXN)
goto nocheck;
if (check_excludes(cpuc->event, n0, 1))
@@ -1102,7 +1102,7 @@ static void sparc_pmu_start_txn(const st
{
struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
- cpuhw->group_flag |= PERF_EVENT_TXN_STARTED;
+ cpuhw->group_flag |= PERF_EVENT_TXN;
}
/*
@@ -1114,7 +1114,7 @@ static void sparc_pmu_cancel_txn(const s
{
struct cpu_hw_events *cpuhw = &__get_cpu_var(cpu_hw_events);
- cpuhw->group_flag &= ~PERF_EVENT_TXN_STARTED;
+ cpuhw->group_flag &= ~PERF_EVENT_TXN;
}
/*
@@ -1137,6 +1137,7 @@ static int sparc_pmu_commit_txn(const st
if (sparc_check_constraints(cpuc->event, cpuc->events, n))
return -EAGAIN;
+ cpuhw->group_flag &= ~PERF_EVENT_TXN;
return 0;
}
Index: linux-2.6/arch/x86/kernel/cpu/perf_event.c
===================================================================
--- linux-2.6.orig/arch/x86/kernel/cpu/perf_event.c
+++ linux-2.6/arch/x86/kernel/cpu/perf_event.c
@@ -969,7 +969,7 @@ static int x86_pmu_enable(struct perf_ev
* skip the schedulability test here, it will be peformed
* at commit time(->commit_txn) as a whole
*/
- if (cpuc->group_flag & PERF_EVENT_TXN_STARTED)
+ if (cpuc->group_flag & PERF_EVENT_TXN)
goto out;
ret = x86_pmu.schedule_events(cpuc, n, assign);
@@ -1096,7 +1096,7 @@ static void x86_pmu_disable(struct perf_
* The events never got scheduled and ->cancel_txn will truncate
* the event_list.
*/
- if (cpuc->group_flags & PERF_EVENT_TXN_STARTED)
+ if (cpuc->group_flags & PERF_EVENT_TXN)
return;
x86_pmu_stop(event);
@@ -1388,7 +1388,7 @@ static void x86_pmu_start_txn(const stru
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
- cpuc->group_flag |= PERF_EVENT_TXN_STARTED;
+ cpuc->group_flag |= PERF_EVENT_TXN;
cpuc->n_txn = 0;
}
@@ -1401,7 +1401,7 @@ static void x86_pmu_cancel_txn(const str
{
struct cpu_hw_events *cpuc = &__get_cpu_var(cpu_hw_events);
- cpuc->group_flag &= ~PERF_EVENT_TXN_STARTED;
+ cpuc->group_flag &= ~PERF_EVENT_TXN;
/*
* Truncate the collected events.
*/
@@ -1435,11 +1435,7 @@ static int x86_pmu_commit_txn(const stru
*/
memcpy(cpuc->assign, assign, n*sizeof(int));
- /*
- * Clear out the txn count so that ->cancel_txn() which gets
- * run after ->commit_txn() doesn't undo things.
- */
- cpuc->n_txn = 0;
+ cpuc->group_flag &= ~PERF_EVENT_TXN;
return 0;
}
Index: linux-2.6/include/linux/perf_event.h
===================================================================
--- linux-2.6.orig/include/linux/perf_event.h
+++ linux-2.6/include/linux/perf_event.h
@@ -549,7 +549,10 @@ struct hw_perf_event {
struct perf_event;
-#define PERF_EVENT_TXN_STARTED 1
+/*
+ * Common implementation detail of pmu::{start,commit,cancel}_txn
+ */
+#define PERF_EVENT_TXN 0x1
/**
* struct pmu - generic performance monitoring unit
@@ -563,14 +566,28 @@ struct pmu {
void (*unthrottle) (struct perf_event *event);
/*
- * group events scheduling is treated as a transaction,
- * add group events as a whole and perform one schedulability test.
- * If test fails, roll back the whole group
+ * Group events scheduling is treated as a transaction, add group
+ * events as a whole and perform one schedulability test. If the test
+ * fails, roll back the whole group
*/
+ /*
+ * Start the transaction, after this ->enable() doesn't need
+ * to do schedulability tests.
+ */
void (*start_txn) (const struct pmu *pmu);
- void (*cancel_txn) (const struct pmu *pmu);
+ /*
+ * If ->start_txn() disabled the ->enable() schedulability test
+ * then ->commit_txn() is required to perform one. On success
+ * the transaction is closed. On error the transaction is kept
+ * open until ->cancel_txn() is called.
+ */
int (*commit_txn) (const struct pmu *pmu);
+ /*
+ * Will cancel the transaction, assumes ->disable() is called for
+ * each successfull ->enable() during the transaction.
+ */
+ void (*cancel_txn) (const struct pmu *pmu);
};
/**
Index: linux-2.6/kernel/perf_event.c
===================================================================
--- linux-2.6.orig/kernel/perf_event.c
+++ linux-2.6/kernel/perf_event.c
@@ -668,15 +668,9 @@ group_sched_in(struct perf_event *group_
}
}
- if (!txn)
+ if (!txn || !pmu->commit_txn(pmu))
return 0;
- ret = pmu->commit_txn(pmu);
- if (!ret) {
- pmu->cancel_txn(pmu);
- return 0;
- }
-
group_error:
/*
* Groups can be scheduled in as one unit only, so undo any
--
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