Re: [PATCH 03/11] block: block_bio_complete tracepoint was missing

[Namhyung Kim]

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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