On 5/4/21 6:59 PM, Bart Van Assche wrote: > On 5/4/21 6:12 AM, Hannes Reinecke wrote: >> On 5/4/21 12:55 PM, John Garry wrote: >>> On 04/05/2021 07:17, Hannes Reinecke wrote: >>>> On 5/4/21 5:20 AM, Bart Van Assche wrote: >>>>> On 5/3/21 8:03 AM, Hannes Reinecke wrote: >>>>>> These commands are set aside before allocating the block-mq tag >>>>>> bitmap, >>>>>> so they'll never show up as busy in the tag map. >>>>> >>>>> That doesn't sound correct to me. Should the above perhaps be changed >>>>> into "blk_mq_start_request() is never called for internal commands so >>>>> they'll never show up as busy in the tag map"? >>>>> >>>> Yes, will do. >>> >>> So why don't these - or shouldn't these - turn up in the busy tag map? >>> >>> One of the motivations to use these block requests for internal >>> commands is that we can take advantage of the block layer handling for >>> CPU hotplug for MQ hosts, i.e. if blk-mq can't see these are inflight, >>> then they would be missed in blk_mq_hctx_notify_offline() -> >>> blk_mq_hctx_has_requests(), right? And who knows what else... >>> >> Oh, but of course it's possible to call 'start' on these requests to >> have them counted in the busy map. >> I just didn't see the need for it until now, that's all. > > This is possible but this will require careful review of at least the > following code paths such that nothing unexpected happens for internal > commands: > * The SCSI timeout code. > * All blk_mq_tagset_busy_iter() and scsi_host_busy_iter() callers. As an > example, scsi_host_busy() must not include LLD-internal commands. > Oh, _that_ is easy. These are reserved commands, which will have the last bool argument to the iter functions set to 'true'. bool (*fn)(struct scsi_cmnd *, void *, bool) So we just need to return from the iter if the last argument is true. Cheers, Hannes -- Dr. Hannes Reinecke Kernel Storage Architect hare@xxxxxxx +49 911 74053 688 SUSE Software Solutions Germany GmbH, 90409 Nürnberg GF: F. Imendörffer, HRB 36809 (AG Nürnberg)
