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

From: Wu Fengguang <fengguang.wu@intel.com>
To: Jan Kara <jack@suse.cz>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Andi Kleen <andi@firstfloor.org>, Ingo Molnar <mingo@elte.hu>,
	Jens Axboe <axboe@kernel.dk>,
	Steven Rostedt <rostedt@goodmis.org>,
	Peter Zijlstra <a.p.zijlstra@chello.nl>,
	Rik van Riel <riel@redhat.com>,
	Linux Memory Management List <linux-mm@kvack.org>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Christoph Hellwig <hch@infradead.org>,
	Dave Chinner <david@fromorbit.com>
Subject: Re: [PATCH 7/9] readahead: add vfs/readahead tracing event
Date: Wed, 30 Nov 2011 20:06:31 +0800	[thread overview]
Message-ID: <20111130120631.GB19834@localhost> (raw)
In-Reply-To: <20111130114438.GD4541@quack.suse.cz>

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@elte.hu>
> > > > CC: Jens Axboe <axboe@kernel.dk>
> > > > CC: Steven Rostedt <rostedt@goodmis.org>
> > > > CC: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > > > Acked-by: Rik van Riel <riel@redhat.com>
> > > > Signed-off-by: Wu Fengguang <fengguang.wu@intel.com>
> > >   Looks OK.
> > > 
> > >   Acked-by: Jan Kara <jack@suse.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