linux-kernel - Re: [PATCH 3/6] perf_counter: per event wakeups

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Message-ID: <20090402113234.GE10828@elte.hu>
Date:	Thu, 2 Apr 2009 13:32:34 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/6] perf_counter: per event wakeups


* Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> By request, provide a way to request a wakeup every 'n' events instead
> of every page of output.
> 
> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> ---
>  include/linux/perf_counter.h |    3 ++-
>  kernel/perf_counter.c        |   10 +++++++++-
>  2 files changed, 11 insertions(+), 2 deletions(-)
> 
> Index: linux-2.6/include/linux/perf_counter.h
> ===================================================================
> --- linux-2.6.orig/include/linux/perf_counter.h
> +++ linux-2.6/include/linux/perf_counter.h
> @@ -146,7 +146,7 @@ struct perf_counter_hw_event {
>  				__reserved_1   : 52;
>  
>  	__u32			extra_config_len;
> -	__u32			__reserved_4;
> +	__u32			wakeup_events;	/* wakeup every n events */

[ Sidenote: i think we need more reserved bits :-) Expand the ABI
  while it's still easy ;-) ]

I have a design observation here:

i think 'wakeup' is a user-space notification type. Another type of 
notication can be 'signal', or 'none'.

Perhaps your current scheme makes the most sense: to treat them as 
separate attributes, and allow signal delivery and wakeups at once. 
(if user-space so wishes)

Agreed?

	Ingo
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