[dm-devel] [PATCH 10/11] block: use block_bio class for getrq and sleeprq

[Christoph Hellwig]

On Wed, Jul 01, 2020 at 04:45:03AM +0000, Chaitanya Kulkarni wrote:
> On 6/29/20 10:13 PM, Christoph Hellwig wrote:
> > On Mon, Jun 29, 2020 at 04:43:13PM -0700, Chaitanya Kulkarni wrote:
> >> The only difference in block_get_rq and block_bio was the last param
> >> passed  __entry->nr_sector & bio->bi_iter.bi_size respectively. Since
> >> that is not the case anymore replace block_get_rq class with block_bio
> >> for block_getrq and block_sleeprq events, also adjust the code to handle
> >> null bio case in block_bio.
> > To me it seems like keeping the NULL bio case separate actually is a
> > little simpler..
> > 
> > 
> 
> Keeping it separate will have an extra event class and related
> event(s) for only handling null bio case.
> 
> Also the block_get_rq class uses 4 comparisons with ?:.
> This patch reduces it to only one comparison in fast path.
> 
> With above explanation does it make sense to get rid of the
> blk_get_rq ?

Without this we don't need the request_queue argument to the bio
class, as we can derive it from the bio, and don't have any
conditionals at all.  I'd rather keep the special case with a 
queue and an optional bio separate.