Hello Thanks for sending this. I too believe this is how it works and given the current performance of OiS it's certainly not single threaded per iSCSI session, and with multiple iSCSI sessions over different NICs, connecting into multipathd, performance and redundancy needs are met for the vast majority of SAN applications.
Often the bottleneck is the backend storage given the interface speeds available today for iSCSI. Especially as you add more hosts. since the IO load as seen by storage is typically very random. Regards, Don On Thu, Jan 23, 2020 at 4:51 PM The Lee-Man <[email protected]> wrote: > On Wednesday, January 15, 2020 at 7:16:48 AM UTC-8, Bobby wrote: >> >> >> Hi all, >> >> I have a question regarding multi-queue in iSCSI. AFAIK, *scsi-mq* has >> been functional in kernel since kernel 3.17. Because earlier, >> the block layer was updated to multi-queue *blk-mq* from single-queue. >> So the current kernel has full-fledged *multi-queues*. >> >> The question is: >> >> How an iSCSI initiator uses multi-queue? Does it mean having multiple >> connections? I would like >> to see where exactly that is achieved in the code, if someone can please >> me give me a hint. Thanks in advance :) >> >> Regards >> > > open-iscsi does not use multi-queue specifically, though all of the block > layer is now converted to using multi-queue. If I understand correctly, > there is no more single-queue, but there is glue that allows existing > single-queue drivers to continue on, mapping their use to multi-queue. > (Someone please correct me if I'm wrong.) > > The only time multi-queue might be useful for open-iscsi to use would be > for MCS -- multiple connections per session. But the implementation of > multi-queue makes using it for MCS problematic. Because each queue is on a > different CPU, open-iscsi would have to coordinate the multiple connections > across multiple CPUs, making things like ensuring correct sequence numbers > difficult. > > Hope that helps. I _believe_ there is still an effort to map open-iscsi > MCS to multi-queue, but nobody has tried to actually do it yet that I know > of. The goal, of course, is better throughput using MCS. > > -- > You received this message because you are subscribed to the Google Groups > "open-iscsi" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to [email protected]. > To view this discussion on the web visit > https://groups.google.com/d/msgid/open-iscsi/8f236c4a-a207-4a0e-8dff-ad14a74e57dc%40googlegroups.com > <https://groups.google.com/d/msgid/open-iscsi/8f236c4a-a207-4a0e-8dff-ad14a74e57dc%40googlegroups.com?utm_medium=email&utm_source=footer> > . > -- You received this message because you are subscribed to the Google Groups "open-iscsi" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To view this discussion on the web visit https://groups.google.com/d/msgid/open-iscsi/CAK3e-EbuwXpvxzTnaGtq3URrfhC4aUvX0%2B4zKat3A2STrON5%3Dg%40mail.gmail.com.
