On Thu, Mar 08, 2018 at 03:34:31PM +0530, Kashyap Desai wrote: > > -----Original Message----- > > From: Ming Lei [mailto:ming.lei@xxxxxxxxxx] > > Sent: Thursday, March 8, 2018 6:46 AM > > To: Kashyap Desai > > Cc: Jens Axboe; linux-block@xxxxxxxxxxxxxxx; Christoph Hellwig; Mike > Snitzer; > > linux-scsi@xxxxxxxxxxxxxxx; Hannes Reinecke; Arun Easi; Omar Sandoval; > > Martin K . Petersen; James Bottomley; Christoph Hellwig; Don Brace; > Peter > > Rivera; Laurence Oberman > > Subject: Re: [PATCH V3 8/8] scsi: megaraid: improve scsi_mq performance > via > > .host_tagset > > > > On Wed, Mar 07, 2018 at 10:58:34PM +0530, Kashyap Desai wrote: > > > > > > > > > > Also one observation using V3 series patch. I am seeing below > > > > > Affinity mapping whereas I have only 72 logical CPUs. It means we > > > > > are really not going to use all reply queues. > > > > > e.a If I bind fio jobs on CPU 18-20, I am seeing only one reply > > > > > queue is used and that may lead to performance drop as well. > > > > > > > > If the mapping is in such shape, I guess it should be quite > > > > difficult to > > > figure out > > > > one perfect way to solve this situation because one reply queue has > > > > to > > > handle > > > > IOs submitted from 4~5 CPUs at average. > > > > > > 4.15.0-rc1 kernel has below mapping - I am not sure which commit id in > " > > > linux_4.16-rc-host-tags-v3.2" is changing the mapping of IRQ to CPU. > > > It > > > > I guess the mapping you posted is read from /proc/irq/126/smp_affinity. > > > > If yes, no any patch in linux_4.16-rc-host-tags-v3.2 should change IRQ > affinity > > code, which is done in irq_create_affinity_masks(), as you saw, no any > patch > > in linux_4.16-rc-host-tags-v3.2 touches that code. > > > > Could you simply apply the patches in linux_4.16-rc-host-tags-v3.2 > against > > 4.15-rc1 kernel and see any difference? > > > > > will be really good if we can fall back to below mapping once again. > > > Current repo linux_4.16-rc-host-tags-v3.2 is giving lots of random > > > mapping of CPU - MSIx. And that will be problematic in performance > run. > > > > > > As I posted earlier, latest repo will only allow us to use *18* reply > > > > Looks not see this report before, could you share us how you conclude > that? > > The only patch changing reply queue is the following one: > > > > https://marc.info/?l=linux-block&m=151972611911593&w=2 > > > > But not see any issue in this patch yet, can you recover to 72 reply > queues > > after reverting the patch in above link? > Ming - > > While testing, my system went bad. I debug further and understood that > affinity mapping was changed due to below commit - > 84676c1f21e8ff54befe985f4f14dc1edc10046b > > [PATCH] genirq/affinity: assign vectors to all possible CPUs > > Because of above change, we end up using very less reply queue. Many reply > queues on my setup was mapped to offline/not-available CPUs. This may be > primary contributing to odd performance impact and it may not be truly due > to V3/V4 patch series. Seems a good news, :-) > > I am planning to check your V3 and V4 series after removing above commit > ID (for performance impact.). You can run your test on a server in which all CPUs are kept as online for avoiding this issue. Or you can apply the following patchset for avoiding this issue: https://marc.info/?l=linux-block&m=152050646332092&w=2 > > It is good if we spread possible CPUs (instead of online cpus) to all irq > vectors considering - We should have at least *one* online CPU mapped to > the vector. Right, that is exactly what the above patchset does. Thanks, Ming
