linux-kernel - Re: [PATCH 03/16] perf, persistent: Setting default buffer size to 512k as in perf tools

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Message-ID: <20130531090718.GD14076@nazgul.tnic>
Date:	Fri, 31 May 2013 11:07:18 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Robert Richter <rric@...nel.org>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	linux-kernel@...r.kernel.org,
	Robert Richter <robert.richter@...xeda.com>
Subject: Re: [PATCH 03/16] perf, persistent: Setting default buffer size to
 512k as in perf tools

On Fri, May 31, 2013 at 10:47:23AM +0200, Robert Richter wrote:
> From: Robert Richter <robert.richter@...xeda.com>
> 
> The default buffer size used to setup event buffers with perf tools is
> 512k. Using the same buffer size for persistent events. This also
> avoids failed mmap calls due to different buffer sizes.
> 
> Signed-off-by: Robert Richter <robert.richter@...xeda.com>
> ---
>  kernel/events/persistent.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/events/persistent.c b/kernel/events/persistent.c
> index 9075164..1e6c03a 100644
> --- a/kernel/events/persistent.c
> +++ b/kernel/events/persistent.c
> @@ -5,6 +5,9 @@
>  
>  #include "internal.h"
>  
> +/* 512 kiB: default perf tools memory size, see perf_evlist__mmap() */
> +#define CPU_BUFFER_NR_PAGES	((512 * 1024) / PAGE_SIZE)
> +
>  static DEFINE_PER_CPU(struct list_head, pers_events);
>  
>  static struct perf_event *
> @@ -151,7 +154,7 @@ int perf_add_persistent_event_by_id(int id)
>  	attr->type		= PERF_TYPE_TRACEPOINT;
>  	attr->size		= sizeof(*attr);
>  
> -	return perf_add_persistent_event(attr, 4);
> +	return perf_add_persistent_event(attr, CPU_BUFFER_NR_PAGES);

This one too - the 4 pages I chose then was purely arbitrary for I had
no idea what size to pick. This clearly makes more sense.

Thanks.
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