linux-kernel - Re: [RFC][PATCH] convert block trace points to TRACE

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Date:	Tue, 19 May 2009 19:33:35 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
Cc:	hch@...radead.org, jmoyer@...hat.com, lizf@...fujitsu.com,
	mingo@...e.hu, rostedt@...dmis.org, fweisbec@...il.com,
	tzanussi@...il.com, tytso@....edu, swhiteho@...hat.com,
	kosaki.motohiro@...fujitsu.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] convert block trace points to TRACE_EVENT()

On Wed, May 20 2009, FUJITA Tomonori wrote:
> On Tue, 19 May 2009 09:08:41 -0400
> Christoph Hellwig <hch@...radead.org> wrote:
> 
> > On Tue, May 19, 2009 at 08:59:29AM -0400, Jeff Moyer wrote:
> > > I'm not sure I'm comfortable with this.  Having had to diagnose
> > > performance problems using blktrace, I find the dev_t information for
> > > plugs and unplugs especially interesting.  Maybe we can still figure
> > > this out given the context in the trace, though.  Can you comment on
> > > that?
> > 
> > The problem is that right now we still allow request queues shared by
> > multiple gendisks, so we can't get at the gendisk.  The blktrace ioctl
> > interface gets around that by doing the setup with an ioctl on the
> > block device node and storing the dev_t at that point.
> > 
> > But I don't think we actually have any drivers left sharing a queue
> > that way, and I'd love to get rid of that for various reasons.
> 
> There are still some (e.g. drivers/block/floppy.c)? I though that we
> hit this when we tried to add the command filter feature though I
> might be wrong (I can't recall).

And mtd, iirc. But only a few. I'll fiddle up a patch to finally get rid
of this, it has been pending for... years.

-- 
Jens Axboe

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