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Date: Wed, 14 Jan 2015 14:29:31 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kan Liang <kan.liang@...el.com>
Cc: eranian@...gle.com, linux-kernel@...r.kernel.org, mingo@...hat.com,
paulus@...ba.org, acme@...nel.org, jolsa@...hat.com,
ak@...ux.intel.com, mikey@...ling.org, anton@...ba.org
Subject: Re: [PATCH V8 03/14] perf, x86: use context switch callback to flush
LBR stack
On Thu, Nov 06, 2014 at 09:54:20AM -0500, Kan Liang wrote:
> --- a/kernel/events/core.c
> @@ -2673,64 +2666,6 @@ static void perf_event_context_sched_in(struct perf_event_context *ctx,
> }
>
> /*
> - * When sampling the branck stack in system-wide, it may be necessary
> - * to flush the stack on context switch. This happens when the branch
> - * stack does not tag its entries with the pid of the current task.
> - * Otherwise it becomes impossible to associate a branch entry with a
> - * task. This ambiguity is more likely to appear when the branch stack
> - * supports priv level filtering and the user sets it to monitor only
> - * at the user level (which could be a useful measurement in system-wide
> - * mode). In that case, the risk is high of having a branch stack with
> - * branch from multiple tasks. Flushing may mean dropping the existing
> - * entries or stashing them somewhere in the PMU specific code layer.
> - *
> - * This function provides the context switch callback to the lower code
> - * layer. It is invoked ONLY when there is at least one system-wide context
> - * with at least one active event using taken branch sampling.
> - */
> -static void perf_branch_stack_sched_in(struct task_struct *prev,
> - struct task_struct *task)
> -{
> - struct perf_cpu_context *cpuctx;
> - struct pmu *pmu;
> - unsigned long flags;
> -
> - /* no need to flush branch stack if not changing task */
> - if (prev == task)
> - return;
> -
> - local_irq_save(flags);
> -
> - rcu_read_lock();
> -
> - list_for_each_entry_rcu(pmu, &pmus, entry) {
> - cpuctx = this_cpu_ptr(pmu->pmu_cpu_context);
> -
> - /*
> - * check if the context has at least one
> - * event using PERF_SAMPLE_BRANCH_STACK
> - */
> - if (cpuctx->ctx.nr_branch_stack > 0
> - && pmu->flush_branch_stack) {
> -
> - perf_ctx_lock(cpuctx, cpuctx->task_ctx);
> -
> - perf_pmu_disable(pmu);
> -
> - pmu->flush_branch_stack();
> -
> - perf_pmu_enable(pmu);
> -
> - perf_ctx_unlock(cpuctx, cpuctx->task_ctx);
> - }
> - }
> -
> - rcu_read_unlock();
> -
> - local_irq_restore(flags);
> -}
So while this patch removes almost everything flush_branch_stack related
it leaves a few rudiments and a broken architecture.
---
Subject: perf,powerpc: Fix up flush_branch_stack users
From: Peter Zijlstra <peterz@...radead.org>
Date: Wed Jan 14 14:15:39 CET 2015
The recent LBR rework for x86 left a stray flush_branch_stack user in
the PowerPC code, fix that up.
Cc: Michael Neuling <mikey@...ling.org>
Cc: Anton Blanchard <anton@...ba.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: http://lkml.kernel.org/n/tip-q4y7je45jtnbp7nhu93by9gs@git.kernel.org
---
arch/powerpc/perf/core-book3s.c | 13 +++++++++----
include/linux/perf_event.h | 5 -----
2 files changed, 9 insertions(+), 9 deletions(-)
--- a/arch/powerpc/perf/core-book3s.c
+++ b/arch/powerpc/perf/core-book3s.c
@@ -124,7 +124,7 @@ static unsigned long ebb_switch_in(bool
static inline void power_pmu_bhrb_enable(struct perf_event *event) {}
static inline void power_pmu_bhrb_disable(struct perf_event *event) {}
-static void power_pmu_flush_branch_stack(void) {}
+static void power_pmu_sched_task(struct perf_event_context *ctx, bool sched_in) {}
static inline void power_pmu_bhrb_read(struct cpu_hw_events *cpuhw) {}
static void pmao_restore_workaround(bool ebb) { }
#endif /* CONFIG_PPC32 */
@@ -350,6 +350,7 @@ static void power_pmu_bhrb_enable(struct
cpuhw->bhrb_context = event->ctx;
}
cpuhw->bhrb_users++;
+ perf_sched_cb_inc(event->ctx->pmu);
}
static void power_pmu_bhrb_disable(struct perf_event *event)
@@ -361,6 +362,7 @@ static void power_pmu_bhrb_disable(struc
cpuhw->bhrb_users--;
WARN_ON_ONCE(cpuhw->bhrb_users < 0);
+ perf_sched_cb_dec(event->ctx->pmu);
if (!cpuhw->disabled && !cpuhw->bhrb_users) {
/* BHRB cannot be turned off when other
@@ -375,9 +377,12 @@ static void power_pmu_bhrb_disable(struc
/* Called from ctxsw to prevent one process's branch entries to
* mingle with the other process's entries during context switch.
*/
-static void power_pmu_flush_branch_stack(void)
+static void power_pmu_sched_task(struct perf_event_context *ctx, bool sched_in)
{
- if (ppmu->bhrb_nr)
+ if (!ppmu->bhrb_nr)
+ return;
+
+ if (sched_in)
power_pmu_bhrb_reset();
}
/* Calculate the to address for a branch */
@@ -1901,7 +1906,7 @@ static struct pmu power_pmu = {
.cancel_txn = power_pmu_cancel_txn,
.commit_txn = power_pmu_commit_txn,
.event_idx = power_pmu_event_idx,
- .flush_branch_stack = power_pmu_flush_branch_stack,
+ .sched_task = power_pmu_sched_task,
};
/*
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -255,11 +255,6 @@ struct pmu {
int (*event_idx) (struct perf_event *event); /*optional */
/*
- * flush branch stack on context-switches (needed in cpu-wide mode)
- */
- void (*flush_branch_stack) (void);
-
- /*
* context-switches callback
*/
void (*sched_task) (struct perf_event_context *ctx,
--
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