linux-kernel - Re: [patch 09/17] LTTng instrumentation

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Date:	Wed, 16 Jul 2008 10:35:34 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	akpm@...ux-foundation.org, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Masami Hiramatsu <mhiramat@...hat.com>, linux-mm@...ck.org,
	Dave Hansen <haveblue@...ibm.com>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Hideo AOKI <haoki@...hat.com>,
	Takashi Nishiie <t-nishiie@...css.fujitsu.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
Subject: Re: [patch 09/17] LTTng instrumentation - filemap

On Tue, 2008-07-15 at 18:26 -0400, Mathieu Desnoyers wrote:
> plain text document attachment (lttng-instrumentation-filemap.patch)
> Instrumentation of waits caused by memory accesses on mmap regions.
> 
> Those tracepoints are used by LTTng.
> 
> About the performance impact of tracepoints (which is comparable to markers),
> even without immediate values optimizations, tests done by Hideo Aoki on ia64
> show no regression. His test case was using hackbench on a kernel where
> scheduler instrumentation (about 5 events in code scheduler code) was added.
> See the "Tracepoints" patch header for performance result detail.
> 
> Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
> CC: linux-mm@...ck.org
> CC: Dave Hansen <haveblue@...ibm.com>
> CC: Masami Hiramatsu <mhiramat@...hat.com>
> CC: 'Peter Zijlstra' <peterz@...radead.org>
> CC: "Frank Ch. Eigler" <fche@...hat.com>
> CC: 'Ingo Molnar' <mingo@...e.hu>
> CC: 'Hideo AOKI' <haoki@...hat.com>
> CC: Takashi Nishiie <t-nishiie@...css.fujitsu.com>
> CC: 'Steven Rostedt' <rostedt@...dmis.org>
> CC: Eduard - Gabriel Munteanu <eduard.munteanu@...ux360.ro>
> ---
>  include/trace/filemap.h |   13 +++++++++++++
>  mm/filemap.c            |    3 +++
>  2 files changed, 16 insertions(+)
> 
> Index: linux-2.6-lttng/mm/filemap.c
> ===================================================================
> --- linux-2.6-lttng.orig/mm/filemap.c	2008-07-15 14:51:50.000000000 -0400
> +++ linux-2.6-lttng/mm/filemap.c	2008-07-15 15:14:46.000000000 -0400
> @@ -33,6 +33,7 @@
>  #include <linux/cpuset.h>
>  #include <linux/hardirq.h> /* for BUG_ON(!in_atomic()) only */
>  #include <linux/memcontrol.h>
> +#include <trace/filemap.h>
>  #include "internal.h"
>  
>  /*
> @@ -541,9 +542,11 @@ void wait_on_page_bit(struct page *page,
>  {
>  	DEFINE_WAIT_BIT(wait, &page->flags, bit_nr);
>  
> +	trace_filemap_wait_start(page, bit_nr);
>  	if (test_bit(bit_nr, &page->flags))
>  		__wait_on_bit(page_waitqueue(page), &wait, sync_page,
>  							TASK_UNINTERRUPTIBLE);
> +	trace_filemap_wait_end(page, bit_nr);
>  }
>  EXPORT_SYMBOL(wait_on_page_bit);

I don't like the trace_filemap_wait_* naming..

trace_wait_on_page_* might make more sense

> Index: linux-2.6-lttng/include/trace/filemap.h
> ===================================================================
> --- /dev/null	1970-01-01 00:00:00.000000000 +0000
> +++ linux-2.6-lttng/include/trace/filemap.h	2008-07-15 15:14:46.000000000 -0400
> @@ -0,0 +1,13 @@
> +#ifndef _TRACE_FILEMAP_H
> +#define _TRACE_FILEMAP_H
> +
> +#include <linux/tracepoint.h>
> +
> +DEFINE_TRACE(filemap_wait_start,
> +	TPPROTO(struct page *page, int bit_nr),
> +	TPARGS(page, bit_nr));
> +DEFINE_TRACE(filemap_wait_end,
> +	TPPROTO(struct page *page, int bit_nr),
> +	TPARGS(page, bit_nr));
> +
> +#endif
> 

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