linux-kernel - Re: [PATCH 7/9] readahead: add vfs/readahead tracing event

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Message-ID: <20111130120631.GB19834@localhost>
Date:	Wed, 30 Nov 2011 20:06:31 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	Jan Kara <jack@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Jens Axboe <axboe@...nel.dk>,
	Steven Rostedt <rostedt@...dmis.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Rik van Riel <riel@...hat.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Dave Chinner <david@...morbit.com>
Subject: Re: [PATCH 7/9] readahead: add vfs/readahead tracing event

On Wed, Nov 30, 2011 at 07:44:38PM +0800, Jan Kara wrote:
> On Wed 30-11-11 08:42:35, Wu Fengguang wrote:
> > On Tue, Nov 29, 2011 at 11:22:28PM +0800, Jan Kara wrote:
> > > On Tue 29-11-11 21:09:07, Wu Fengguang wrote:
> > > > This is very useful for verifying whether the readahead algorithms are
> > > > working to the expectation.
> > > > 
> > > > Example output:
> > > > 
> > > > # echo 1 > /debug/tracing/events/vfs/readahead/enable
> > > > # cp test-file /dev/null
> > > > # cat /debug/tracing/trace  # trimmed output
> > > > readahead-initial(dev=0:15, ino=100177, req=0+2, ra=0+4-2, async=0) = 4
> > > > readahead-subsequent(dev=0:15, ino=100177, req=2+2, ra=4+8-8, async=1) = 8
> > > > readahead-subsequent(dev=0:15, ino=100177, req=4+2, ra=12+16-16, async=1) = 16
> > > > readahead-subsequent(dev=0:15, ino=100177, req=12+2, ra=28+32-32, async=1) = 32
> > > > readahead-subsequent(dev=0:15, ino=100177, req=28+2, ra=60+60-60, async=1) = 24
> > > > readahead-subsequent(dev=0:15, ino=100177, req=60+2, ra=120+60-60, async=1) = 0
> > > > 
> > > > CC: Ingo Molnar <mingo@...e.hu>
> > > > CC: Jens Axboe <axboe@...nel.dk>
> > > > CC: Steven Rostedt <rostedt@...dmis.org>
> > > > CC: Peter Zijlstra <a.p.zijlstra@...llo.nl>
> > > > Acked-by: Rik van Riel <riel@...hat.com>
> > > > Signed-off-by: Wu Fengguang <fengguang.wu@...el.com>
> > >   Looks OK.
> > > 
> > >   Acked-by: Jan Kara <jack@...e.cz>
> > 
> > Thank you.
> > 
> > > > +	TP_printk("readahead-%s(dev=%d:%d, ino=%lu, "
> > > > +		  "req=%lu+%lu, ra=%lu+%d-%d, async=%d) = %d",
> > > > +			ra_pattern_names[__entry->pattern],
> > > > +			MAJOR(__entry->dev),
> > > > +			MINOR(__entry->dev),
> > 
> > One thing I'm not certain is the dev=MAJOR:MINOR. The other option
> > used in many trace events are bdi=BDI_NAME_OR_NUMBER. Will bdi be more
> > suitable here?
>   Probably bdi name will be more consistent (e.g. with writeback) but I
> don't think it makes a big difference in practice.

Yeah, so I'll change to bdi name.

Thanks,
Fengguang
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