On Fri, Oct 25, 2019 at 05:33:35PM +0100, John Garry wrote: > > > There might be two reasons: > > > > > > 1) You are still testing a multiple reply-queue device? > > > > As before, I am testing by exposing mutliple queues to the SCSI > > midlayer. I had to make this change locally, as on mainline we still > > only expose a single queue and use the internal reply queue when > > enabling managed interrupts. > > > > As I > > > mentioned last times, it is hard to map reply-queue into blk-mq > > > hctx correctly. > > > > Here's my branch, if you want to check: > > > > https://github.com/hisilicon/kernel-dev/commits/private-topic-sas-5.4-mq-v4 > > > > It's a bit messy (sorry), but you can see that the reply-queue in the > > LLDD is removed in commit 087b95af374. > > > > I am now thinking of actually making this change to the LLDD in mainline > > to avoid any doubt in future. > > > > > > > > 2) concurrent dispatch to device, which can be observed by the > > > following patch. > > > > > > diff --git a/block/blk-mq.c b/block/blk-mq.c > > > index 06081966549f..3590f6f947eb 100644 > > > --- a/block/blk-mq.c > > > +++ b/block/blk-mq.c > > > @@ -679,6 +679,8 @@ void blk_mq_start_request(struct request *rq) > > > { > > > struct request_queue *q = rq->q; > > > > > > + WARN_ON_ONCE(test_bit(BLK_MQ_S_INTERNAL_STOPPED, > > > &rq->mq_hctx->state)); > > > + > > > trace_block_rq_issue(q, rq); > > > > > > if (test_bit(QUEUE_FLAG_STATS, &q->queue_flags)) { > > > > > > However, I think it is hard to be 2#, since the current CPU is the last > > > CPU in hctx->cpu_mask. > > > > > > > I'll try it. > > > > Hi Ming, > > I am looking at this issue again. > > I am using https://lore.kernel.org/linux-scsi/1571926881-75524-1-git-send-email-john.garry@xxxxxxxxxx/T/#t > with expose_mq_experimental set. I guess you're going to say that this > series is wrong, but I think it's ok for this purpose. > > Forgetting that for a moment, maybe I have found an issue. > > For the SCSI commands which timeout, I notice that > scsi_set_blocked(reason=SCSI_MLQUEUE_EH_RETRY) was called 30 seconds > earlier. > > scsi_set_blocked+0x20/0xb8 > __scsi_queue_insert+0x40/0x90 > scsi_softirq_done+0x164/0x1c8 > __blk_mq_complete_request_remote+0x18/0x20 > flush_smp_call_function_queue+0xa8/0x150 > generic_smp_call_function_single_interrupt+0x10/0x18 > handle_IPI+0xec/0x1a8 > arch_cpu_idle+0x10/0x18 > do_idle+0x1d0/0x2b0 > cpu_startup_entry+0x24/0x40 > secondary_start_kernel+0x1b4/0x208 Could you investigate a bit the reason why timeout is triggered? Especially we suppose to drain all in-flight requests before the last CPU of this hctx becomes offline, and it shouldn't be caused by the hctx becoming dead, so still need you to confirm that all in-flight requests are really drained in your test. Or is it still possible to dispatch to LDD after BLK_MQ_S_INTERNAL_STOPPED is set? In theory, it shouldn't be possible, given we drain in-flight request on the last CPU of this hctx. Or blk_mq_hctx_next_cpu() may still run WORK_CPU_UNBOUND schedule after all CPUs are offline, could you add debug message in that branch? > > I also notice that the __scsi_queue_insert() call, above, seems to retry to > requeue the request on a dead rq in calling > __scsi_queue_insert()->blk_mq_requeue_requet()->__blk_mq_requeue_request(), > ***: > > [ 1185.235243] psci: CPU1 killed. > [ 1185.238610] blk_mq_hctx_notify_dead cpu1 dead > request_queue=0xffff0023ace24f60 (id=19) > [ 1185.246530] blk_mq_hctx_notify_dead cpu1 dead > request_queue=0xffff0023ace23f80 (id=17) > [ 1185.254443] blk_mq_hctx_notify_dead cpu1 dead > request_queue=0xffff0023ace22fa0 (id=15) > [ 1185.262356] blk_mq_hctx_notify_dead cpu1 dead > request_queue=0xffff0023ace21fc0 (id=13)*** > [ 1185.270271] blk_mq_hctx_notify_dead cpu1 dead > request_queue=0xffff0023ace20fe0 (id=11) > [ 1185.939451] scsi_softirq_done NEEDS_RETRY rq=0xffff0023b7416000 > [ 1185.945359] scsi_set_blocked reason=0x1057 > [ 1185.949444] __blk_mq_requeue_request request_queue=0xffff0023ace21fc0 > id=13 rq=0xffff0023b7416000*** > > [...] > > [ 1214.903455] scsi_timeout req=0xffff0023add29000 reserved=0 > [ 1214.908946] scsi_timeout req=0xffff0023add29300 reserved=0 > [ 1214.914424] scsi_timeout req=0xffff0023add29600 reserved=0 > [ 1214.919909] scsi_timeout req=0xffff0023add29900 reserved=0 > > I guess that we're retrying as the SCSI failed in the LLDD for some reason. > > So could this be the problem - we're attempting to requeue on a dead request > queue? If there are any in-flight requests originated from hctx which is going to become dead, they should have been drained before CPU becomes offline. Thanks, Ming
