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

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Date:	Wed, 20 May 2009 00:49:58 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	hch@...radead.org
Cc:	jmoyer@...hat.com, lizf@...fujitsu.com, mingo@...e.hu,
	jens.axboe@...cle.com, 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 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).
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