Ming, Thanks for checking this request and sending appropriate changes. This RFC changes are settled down with proper block layer changes (below patch) sent by Ming. https://www.spinics.net/lists/linux-block/msg28279.html Kashyap > -----Original Message----- > From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > Sent: Wednesday, July 4, 2018 2:38 PM > To: Kashyap Desai > Cc: linux-block@xxxxxxxxxxxxxxx; Jens Axboe; Omar Sandoval; Christoph > Hellwig; Hannes Reinecke; linux-scsi; Laurence Oberman > Subject: Re: [RFC] bypass scheduler for no sched is set > > On Wed, Jul 04, 2018 at 01:29:50PM +0530, Kashyap Desai wrote: > > Hi, > > > > Ming Lei posted below patch series and performance improved for > > megaraid_sas driver. I used the same kernel base and figure out some more > > possible performance improvement in block layer. This RFC improves > > performance as well as CPU utilization. If this patch fits the design > > aspect of the blk-mq and scsi-mq, I can convert it into PATCH and submit > > the same/modified version. > > > > https://marc.info/?l=linux-block&m=153062994403732&w=2 > > > > Description of change - > > > > Do not insert request into software queue if BLK_MQ_F_NO_SCHED is set. > > Submit request from blk_mq_make_request to low level driver directly as > > depicted through below function call. > > > > blk_mq_try_issue_directly > > > > > > __blk_mq_try_issue_directly > > > > scsi_queue_rq > > Hi Kashyap, > > When I sent you the patches[1] which include 'global tags' support, MegaRAID > is converted to per-node queues and becomes real MQ(q->nr_hw_queues > > 1), IO > should have been issued direclty, please see the branch of '(plug && > !blk_queue_nomerges(q))' and '(q->nr_hw_queues > 1 && is_sync)' in > blk_mq_make_request(). > > But looks not see any improvement from your test result, even though huge > improvement can be observed on null_blk/scsi_debug. Maybe somewhere is > wrong, > and days ago I talked with Laurence about doing this kind of test again. > > I will double check the 'global tags' patches, meantime could you or > Laurence help to check if global tags[2] works in expected way if > you'd like to? > > [1] https://github.com/ming1/linux/commits/v4.16-rc-host-tags-v5 > [2] https://github.com/ming1/linux/commits/v4.18-rc-host-tags-v8 > > > > Low level driver attached to scsi.mq can set BLK_MQ_F_NO_SCHED, If they > do > > not want benefit from io scheduler (e.a in case of SSDs connected to IT/MR > > controller). In case of HDD drives connected to HBA, driver can avoid > > setting BLK_MQ_F_NO_SCHED so that default elevator is set to mq- > deadline. > > That might be one way for improving megaraid_sas. > > However, even for modern high performance device, such as NVMe, turns out > IO scheduler(such as kyber) may play a big role for improving latency or > throughput. > > > Thanks, > Ming
