linux-kernel - Re: [PATCH V5 03/13] perf: Allow pmu to choose cpu on which to install event

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Date:	Tue, 12 Jun 2012 12:17:33 +0200
From:	Stephane Eranian <eranian@...gle.com>
To:	"Yan, Zheng" <zheng.z.yan@...el.com>
Cc:	a.p.zijlstra@...llo.nl, mingo@...e.hu, jolsa@...hat.com,
	andi@...stfloor.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V5 03/13] perf: Allow pmu to choose cpu on which to
 install event

On Tue, Jun 12, 2012 at 7:37 AM, Yan, Zheng <zheng.z.yan@...el.com> wrote:
> From: "Yan, Zheng" <zheng.z.yan@...el.com>
>
> Allow the pmu->event_init callback to change event->cpu, so pmu can
> choose cpu on which to install event.
>
So now, the user can say perf record -e xxxx -C 1 -a and then get nothing
out of perf report -C1 because under the cover the kernel has swapped
it for another CPU?

> Signed-off-by: Zheng Yan <zheng.z.yan@...el.com>
> ---
>  kernel/events/core.c |    8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index d71a2d6..2c05027 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6302,7 +6302,7 @@ SYSCALL_DEFINE5(perf_event_open,
>        /*
>         * Get the target context (task or percpu):
>         */
> -       ctx = find_get_context(pmu, task, cpu);
> +       ctx = find_get_context(pmu, task, event->cpu);
>        if (IS_ERR(ctx)) {
>                err = PTR_ERR(ctx);
>                goto err_alloc;
> @@ -6375,16 +6375,16 @@ SYSCALL_DEFINE5(perf_event_open,
>        mutex_lock(&ctx->mutex);
>
>        if (move_group) {
> -               perf_install_in_context(ctx, group_leader, cpu);
> +               perf_install_in_context(ctx, group_leader, event->cpu);
>                get_ctx(ctx);
>                list_for_each_entry(sibling, &group_leader->sibling_list,
>                                    group_entry) {
> -                       perf_install_in_context(ctx, sibling, cpu);
> +                       perf_install_in_context(ctx, sibling, event->cpu);
>                        get_ctx(ctx);
>                }
>        }
>
> -       perf_install_in_context(ctx, event, cpu);
> +       perf_install_in_context(ctx, event, event->cpu);
>        ++ctx->generation;
>        perf_unpin_context(ctx);
>        mutex_unlock(&ctx->mutex);
> --
> 1.7.10.2
>
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