On Sat, 2018-01-27 at 14:09 -0500, Mike Snitzer wrote: > Ming let me know that he successfully tested this V3 patch using both > your test (fio to both mpath and underlying path) and Bart's (02-mq with > can_queue in guest). > > Would be great if you'd review and verify this fix works for you too. > > Ideally we'd get a fix for this regression staged for 4.16 inclusion. > This V3 patch seems like the best option we have at this point. Hello Mike, There are several issues with the patch at the start of this thread: - It is an unnecessary change of the block layer API. Queue stalls can already be addressed with the current block layer API, namely by inserting a blk_mq_delay_run_hw_queue() call before returning BLK_STS_RESOURCE. - The patch at the start of this thread complicates code further that is already too complicated, namely the blk-mq core. - The patch at the start of this thread introduces a regression in the SCSI core, namely a queue stall if a request completion occurs concurrently with the newly added BLK_MQ_S_SCHED_RESTART test in the blk-mq core. As a kernel maintainer one of your responsibilities is to help keeping the quality of the kernel code high. So I think that you, as a kernel maintainer, should tell Ming to discard this patch instead of asking to merge it upstream given all the disadvantages of this patch. Bart.
