linux-kernel - Re: [PATCH] perf session: Add option to copy events when queueing

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Date:	Wed, 02 Oct 2013 06:52:57 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>
CC:	acme@...stprotocols.net, linux-kernel@...r.kernel.org,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf session: Add option to copy events when queueing

On 10/2/13 6:38 AM, Jiri Olsa wrote:
>>> Examples hitting this problem are 'perf kvm stat live', especially with nested
>>> VMs which generate 100,000+ traces per second, and a command processing
>>> scheduling events with a high rate of context switching -- e.g., running
>>> 'perf bench sched pipe'.
>>>
>>> This patch offers live commands an option to copy the event when it is
>>> placed in
>>> the ordered samples queue.
>
> So I guess you have some other patch that actually sets
> session::copy_on_queue?

Yes, with this patch commands have to set session->copy_on_queue to true.

My latest perf-sched-daemon code actually solves this another way: 
rather than asking perf-session to copy the events, the command itself 
does and passes the copied event to the perf-session processing code.

I like this design better because the command itself controls the 
allocation and free which the daemon needs because the events are added 
to another queue so the flow is:

    read from mmmap --> copy event --> pass to session code for time 
ordering --> process time ordered events

The daemon puts the time ordered events into a time-limited queue and 
only processes the event when requested.

If that is too confusing take a look at:

https://github.com/dsahern/linux/blob/perf-sched-timehist-3.11/tools/perf/schedmon.c

process_event is the handler for sample events coming out of the mmaps. 
It allocates memory, copies the event and then calls 
perf_session_queue_event on the copy.

David

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