linux-kernel - Re: [PATCH] block: trace completion of all bios.

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Date:   Wed, 22 Mar 2017 05:51:49 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     NeilBrown <neilb@...e.com>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-raid@...r.kernel.org, dm-devel@...hat.com,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Shaohua Li <shli@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] block: trace completion of all bios.

On Wed, Mar 22, 2017 at 01:38:09PM +1100, NeilBrown wrote:
> 
> Currently only dm and md/raid5 bios trigger trace_block_bio_complete().
> Now that we have bio_chain(), it is not possible, in general, for a
> driver to know when the bio is really complete.  Only bio_endio()
> knows that.
> 
> So move the trace_block_bio_complete() call to bio_endio().

This will cause duplicate events for request based drivers.  You'll
need to have a bio_endio_notrace or similar without that the request
completion path can call.