linux-kernel - Re: [PATCH 03/11] block: block_bio

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Date:	Mon, 09 Jan 2012 11:33:27 +0900
From:	Namhyung Kim <namhyung.kim@....com>
To:	Tejun Heo <tj@...nel.org>
CC:	Namhyung Kim <namhyung.kim@....com>, axboe@...nel.dk,
	mingo@...hat.com, rostedt@...dmis.org, fweisbec@...il.com,
	teravest@...gle.com, slavapestov@...gle.com, ctalbott@...gle.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/11] block: block_bio_complete tracepoint was missing

Hi,

2012-01-09 10:49 AM, Tejun Heo wrote:
> Hello,
>
> On Mon, Jan 09, 2012 at 10:30:06AM +0900, Namhyung Kim wrote:
>> Just adding the TP unconditionally will produce duplicated (in some
>> sense) reports about the completion. For example, normal request
>> based IO reports whole request completion prior to its bio's, and
>> further
>
> Request and bio completions are separate events.  There's nothing
> wrong with reporting them separately.  In fact, I think they should be
> reported separately.
>
>> , some of nested block IO handling routines - bounced bio and
>> btrfs with compression, etc - call bio_endio() more than once. Also
>> there are cases that bio fails before it's enqueued for some reason.
>
> They are actually separate bio's being completed.  I don't think
> trying to put extra semantics on TP itself is a good idea.  In
> general, TP signals that such event happened with sufficient
> information and it's the consumers' responsibility to make sense of
> what's going on.  BIO_CLONED/BOUNCED are there.

I see.


>> I have no idea about the ioblame can deal with all of such corner
>> cases. However it might confuse blktrace somewhat, I guess.
>
> Unless someone is doing memcpy() on bio's, ioblame should be okay.  It
> only considers bio's which went through actual submission.
>
>> I already posted similar patch a couple of weeks ago, but didn't
>> receive a comment yet. [1] Please take a look this too :)
>
> I'll reply there but don't think imposing such extra logic on TP is a
> good idea.

I'll reply on that thread too. :)


>> After a quick glance, the ioblame seems to carry all IO accounting
>> info through the first bio in the request. If so, why don't you use
>> the request structure for that?
>
> Because there are bio based drivers which don't use requests at all.

What I thought for such drivers was dynamic allocation in their 
->make_request_fn, but because we don't have a block_bio_issue TP, 
Nevermind. :)


Thanks,
Namhyung Kim
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