linux-kernel - Re: [Intel-gfx] [RFC PATCH 03/11] perf: Add PERF_EVENT_IOC

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Message-ID: <20150507142009.GX22099@nuc-i3427.alporthouse.com>
Date:	Thu, 7 May 2015 15:20:09 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Robert Bragg <robert@...bynine.org>
Cc:	intel-gfx@...ts.freedesktop.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	David Airlie <airlied@...ux.ie>, linux-api@...r.kernel.org,
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [Intel-gfx] [RFC PATCH 03/11] perf: Add PERF_EVENT_IOC_FLUSH
 ioctl

On Thu, May 07, 2015 at 03:15:46PM +0100, Robert Bragg wrote:
> To allow for pmus that may have internal buffering (e.g. the hardware
> itself writes out data to its own circular buffer which is only
> periodically forwarded to userspace via perf) this ioctl enables
> userspace to explicitly ensure it has received all samples before a
> point in time.
> 
> Signed-off-by: Robert Bragg <robert@...bynine.org>
> ---
>  include/linux/perf_event.h      | 7 +++++++
>  include/uapi/linux/perf_event.h | 1 +
>  kernel/events/core.c            | 5 +++++
>  3 files changed, 13 insertions(+)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 1af35b4..69a0cb9 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -266,6 +266,13 @@ struct pmu {
>  	 * flush branch stack on context-switches (needed in cpu-wide mode)
>  	 */
>  	void (*flush_branch_stack)	(void);
> +
> +	/*
> +	 * Flush buffered samples (E.g. for pmu hardware that writes samples to
> +	 * some intermediate buffer) userspace may need to explicitly ensure
> +	 * such samples have been forwarded to perf.
> +	 */
> +	void (*flush)			(struct perf_event *event); /*optional */

void return?
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre
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