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Message-ID: <20150901103859.GP19282@twins.programming.kicks-ass.net>
Date: Tue, 1 Sep 2015 12:38:59 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@...hat.com>,
Arnaldo Carvalho de Melo <acme@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v5 1/8] perf: Add a flags parameter to pmu txn interfaces
On Thu, Aug 13, 2015 at 11:49:34PM -0700, Sukadev Bhattiprolu wrote:
I'm ever so sorry I keep going on about this, but..
> diff --git a/arch/powerpc/perf/core-book3s.c b/arch/powerpc/perf/core-book3s.c
> index d90893b..b18efe4 100644
> --- a/arch/powerpc/perf/core-book3s.c
> +++ b/arch/powerpc/perf/core-book3s.c
> @@ -50,6 +50,7 @@ struct cpu_hw_events {
>
> unsigned int group_flag;
> int n_txn_start;
> + int txn_flags;
>
> /* BHRB bits */
> u64 bhrb_filter; /* BHRB HW branch filter */
> @@ -1586,11 +1587,19 @@ static void power_pmu_stop(struct perf_event *event, int ef_flags)
> * Start group events scheduling transaction
> * Set the flag to make pmu::enable() not perform the
> * schedulability test, it will be performed at commit time
> + *
> + * We only support PERF_PMU_TXN_ADD transactions. Save the
> + * transaction flags but otherwise ignore non-PERF_PMU_TXN_ADD
> + * transactions.
> */
> -static void power_pmu_start_txn(struct pmu *pmu)
> +static void power_pmu_start_txn(struct pmu *pmu, int txn_flags)
> {
> struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
>
> + cpuhw->txn_flags = txn_flags;
> + if (txn_flags & ~PERF_PMU_TXN_ADD)
> + return;
> +
> perf_pmu_disable(pmu);
> cpuhw->group_flag |= PERF_EVENT_TXN;
> cpuhw->n_txn_start = cpuhw->n_events;
> @@ -1604,6 +1613,12 @@ static void power_pmu_start_txn(struct pmu *pmu)
> static void power_pmu_cancel_txn(struct pmu *pmu)
> {
> struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
> + int txn_flags;
> +
> + txn_flags = cpuhw->txn_flags;
> + cpuhw->txn_flags = 0;
> + if (txn_flags & ~PERF_PMU_TXN_ADD)
> + return;
>
> cpuhw->group_flag &= ~PERF_EVENT_TXN;
> perf_pmu_enable(pmu);
> @@ -1618,10 +1633,18 @@ static int power_pmu_commit_txn(struct pmu *pmu)
> {
> struct cpu_hw_events *cpuhw;
> long i, n;
> + int txn_flags;
>
> if (!ppmu)
> return -EAGAIN;
> +
> cpuhw = this_cpu_ptr(&cpu_hw_events);
> +
> + txn_flags = cpuhw->txn_flags;
> + cpuhw->txn_flags = 0;
> + if (cpuhw->txn_flags & ~PERF_PMU_TXN_ADD)
> + return 0;
> +
> n = cpuhw->n_events;
> if (check_excludes(cpuhw->event, cpuhw->flags, 0, n))
> return -EAGAIN;
when looking at this (I almost pressed A for apply) it occurred to me
that we now keep double state, cpuhw->txn_flags and cpuhw->group_flag
are basically the same thing.
Would not something like the below avoid this duplication?
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -48,9 +48,8 @@ struct cpu_hw_events {
unsigned long amasks[MAX_HWEVENTS][MAX_EVENT_ALTERNATIVES];
unsigned long avalues[MAX_HWEVENTS][MAX_EVENT_ALTERNATIVES];
- unsigned int group_flag;
+ unsigned int txn_flags;
int n_txn_start;
- int txn_flags;
/* BHRB bits */
u64 bhrb_filter; /* BHRB HW branch filter */
@@ -1442,7 +1441,7 @@ static int power_pmu_add(struct perf_eve
* skip the schedulability test here, it will be performed
* at commit time(->commit_txn) as a whole
*/
- if (cpuhw->group_flag & PERF_EVENT_TXN)
+ if (cpuhw->txn_flags & PERF_PMU_TXN_ADD)
goto nocheck;
if (check_excludes(cpuhw->event, cpuhw->flags, n0, 1))
@@ -1596,12 +1595,12 @@ static void power_pmu_start_txn(struct p
{
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
+ WARN_ON_ONCE(cpuhw->txn_flags); /* already txn in flight */
cpuhw->txn_flags = txn_flags;
if (txn_flags & ~PERF_PMU_TXN_ADD)
return;
perf_pmu_disable(pmu);
- cpuhw->group_flag |= PERF_EVENT_TXN;
cpuhw->n_txn_start = cpuhw->n_events;
}
@@ -1615,12 +1614,12 @@ static void power_pmu_cancel_txn(struct
struct cpu_hw_events *cpuhw = this_cpu_ptr(&cpu_hw_events);
int txn_flags;
+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
txn_flags = cpuhw->txn_flags;
cpuhw->txn_flags = 0;
if (txn_flags & ~PERF_PMU_TXN_ADD)
return;
- cpuhw->group_flag &= ~PERF_EVENT_TXN;
perf_pmu_enable(pmu);
}
@@ -1633,17 +1632,17 @@ static int power_pmu_commit_txn(struct p
{
struct cpu_hw_events *cpuhw;
long i, n;
- int txn_flags;
if (!ppmu)
return -EAGAIN;
cpuhw = this_cpu_ptr(&cpu_hw_events);
- txn_flags = cpuhw->txn_flags;
- cpuhw->txn_flags = 0;
- if (cpuhw->txn_flags & ~PERF_PMU_TXN_ADD)
+ WARN_ON_ONCE(!cpuhw->txn_flags); /* no txn in flight */
+ if (cpuhw->txn_flags & ~PERF_PMU_TXN_ADD) {
+ cpuhw->txn_flags = 0;
return 0;
+ }
n = cpuhw->n_events;
if (check_excludes(cpuhw->event, cpuhw->flags, 0, n))
@@ -1655,7 +1654,7 @@ static int power_pmu_commit_txn(struct p
for (i = cpuhw->n_txn_start; i < n; ++i)
cpuhw->event[i]->hw.config = cpuhw->events[i];
- cpuhw->group_flag &= ~PERF_EVENT_TXN;
+ cpuhw->txn_flags = 0;
perf_pmu_enable(pmu);
return 0;
}
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -199,9 +199,7 @@ struct perf_event;
/*
* Common implementation detail of pmu::{start,commit,cancel}_txn
*/
-#define PERF_EVENT_TXN 0x1
-
-#define PERF_PMU_TXN_ADD 0x1 /* txn to add/schedule event on PMU */
+#define PERF_PMU_TXN_ADD 0x1 /* txn to add/schedule event on PMU */
/**
* pmu::capabilities flags
--
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