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Message-ID: <37D7C6CF3E00A74B8858931C1DB2F0770169FC39@SHSMSX103.ccr.corp.intel.com>
Date: Wed, 14 Jan 2015 14:16:08 +0000
From: "Liang, Kan" <kan.liang@...el.com>
To: Peter Zijlstra <peterz@...radead.org>
CC: "eranian@...gle.com" <eranian@...gle.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"mingo@...hat.com" <mingo@...hat.com>,
"paulus@...ba.org" <paulus@...ba.org>,
"acme@...nel.org" <acme@...nel.org>,
"jolsa@...hat.com" <jolsa@...hat.com>,
"ak@...ux.intel.com" <ak@...ux.intel.com>,
"mikey@...ling.org" <mikey@...ling.org>,
"anton@...ba.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.
Thanks for providing this patch to fix the issue.
Kan
>
> ---
> 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@....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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