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

[Jan Kara]

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@xxxxxxx>
> > > CC: Jens Axboe <axboe@xxxxxxxxx>
> > > CC: Steven Rostedt <rostedt@xxxxxxxxxxx>
> > > CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
> > > Acked-by: Rik van Riel <riel@xxxxxxxxxx>
> > > Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
> >   Looks OK.
> > 
> >   Acked-by: Jan Kara <jack@xxxxxxx>
> 
> 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.

								Honza
-- 
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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