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

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Date:   Thu, 23 Mar 2017 17:26:11 +1100
From:   NeilBrown <neilb@...e.com>
To:     Christoph Hellwig <hch@...radead.org>
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, Christoph Hellwig wrote:

> 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.

Ah... I hadn't noticed that the request completion was the same event
type as the bio completion...  Thanks.  Also after being processed by the
request handler, bi_sector and bi_size have changed so the trace
messsage would be wrong.

I've sorted that out and will repost.

Thanks,
NeilBrown



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