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. Sinan -- Sinan Kaya Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc. Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project. -- 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
