On Mon, Jul 17, 2017 at 06:46:11PM -0400, Sinan Kaya wrote: > Hi Keith, > > On 7/17/2017 6:45 PM, Keith Busch wrote: > > On Mon, Jul 17, 2017 at 06:36:23PM -0400, Sinan Kaya wrote: > >> Code is moving the completion queue doorbell after processing all completed > >> events and sending callbacks to the block layer on each iteration. > >> > >> This is causing a performance drop when a lot of jobs are queued towards > >> the HW. Move the completion queue doorbell on each loop instead and allow new > >> jobs to be queued by the HW. > > > > That doesn't make sense. Aggregating doorbell writes should be much more > > efficient for high depth workloads. > > > > Problem is that code is throttling the HW as HW cannot queue more completions until > SW get a chance to clear it. > > As an example: > > for each in N > ( > blk_layer() > ) > ring door bell > > HW cannot queue new job until N x blk_layer operations are processed and queue > element ownership is passed to the HW after the loop. HW is just sitting idle > there if no queue entries are available. If no completion queue entries are available, then there can't possibly be any submission queue entries for the HW to work on either. -- To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
