linux-kernel - Re: [RFC][PATCH 5/9] perf: Simplify and fix __perf_install_in

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Date:	Mon, 11 Apr 2011 16:12:31 +0800
From:	Lin Ming <ming.m.lin@...el.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Oleg Nesterov <oleg@...hat.com>, Jiri Olsa <jolsa@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [RFC][PATCH 5/9] perf: Simplify and fix
 __perf_install_in_context

On Sat, 2011-04-09 at 21:17 +0200, Peter Zijlstra wrote:
> plain text document attachment (perf_install_in_context.patch)
> Currently __perf_install_in_context() will try and schedule in the
> event irrespective of our event scheduling rules, that is, we try to
> schedule CPU-pinned, TASK-pinned, CPU-flexible, TASK-flexible, but
> when creating a new event we simply try and schedule it on top of
> whatever is already on the PMU, this can lead to errors for pinned
> events.
> 
> Therefore, simplify things and simply schedule everything out, add the
> event to the corresponding context and schedule everything back in.
> 
> This also nicely handles the case where with
> __ARCH_WANT_INTERRUPTS_ON_CTXSW the IPI can come right in the middle
> of schedule, before we managed to call perf_event_task_sched_in().
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  kernel/perf_event.c |   80 ++++++++++++++++++++++------------------------------
>  1 file changed, 35 insertions(+), 45 deletions(-)
> 
> Index: linux-2.6/kernel/perf_event.c
> ===================================================================
> --- linux-2.6.orig/kernel/perf_event.c
> +++ linux-2.6/kernel/perf_event.c
> @@ -1476,8 +1476,12 @@ static void add_event_to_ctx(struct perf
>  	event->tstamp_stopped = tstamp;
>  }
>  
> -static void perf_event_context_sched_in(struct perf_event_context *ctx,
> -					struct task_struct *tsk);
> +static void task_ctx_sched_out(struct perf_event_context *ctx);
> +static void
> +ctx_sched_in(struct perf_event_context *ctx,
> +	     struct perf_cpu_context *cpuctx,
> +	     enum event_type_t event_type,
> +	     struct task_struct *task);
>  
>  /*
>   * Cross CPU call to install and enable a performance event
> @@ -1488,20 +1492,31 @@ static int  __perf_install_in_context(vo
>  {
>  	struct perf_event *event = info;
>  	struct perf_event_context *ctx = event->ctx;
> -	struct perf_event *leader = event->group_leader;
>  	struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
> -	int err;
> +	struct perf_event_context *task_ctx = cpuctx->task_ctx;
> +	struct task_struct *task = current;
> +
> +	perf_ctx_lock(cpuctx, cpuctx->task_ctx);

perf_ctx_lock(cpuctx, task_ctx)

since task_ctx is assigned with cpuctx->task_ctx.

Lin Ming

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