Re: [patch] nd_blk,nd_pmem,nd_btt: add endio blktrace events

[Christoph Hellwig <hch@infradead.org>]

On Wed, Nov 09, 2016 at 02:43:58PM -0500, Jeff Moyer wrote:
> But on the issue side, we have different trace actions: Q vs. I.  On the
> completion side, we just have C.  You'd end up getting two C events for
> each Q, and that may confuse existing utilities (such as blkparse, btt,
> iowatcher, fio, etc), not to mention any scripts built around the
> tracepoints, and any users looking at the raw blkparse output.
> 
> So, are you suggesting we add another action on the endio side?  If so,
> that's a different patch set.  ;-)  If you're suggesting this multiple C
> event thing, I'm not on board with that.

Ok, good point.  It's a little bit annoying how asymetic the tracepoints
are, but fixing it now might cause more harm than it helps.

That being said, it might still be a good idea to have bio_endio call
the tracepoint, we'll just need a __bio_endio to bypass the tracepoints
for calls from the request layer.  That way all bio-based drivers will
automatically do the right thing.