On 11/13/18 2:56 AM, Jianchao Wang wrote: > When issue request directly and the task is migrated out of the > original cpu where it allocates request, hctx could be ran on > the cpu where it is not mapped. > To fix this, > - insert the request forcibly if BLK_MQ_F_BLOCKING is set. > - check whether the current is mapped to the hctx, if not, insert > forcibly. > - invoke __blk_mq_issue_directly under preemption disabled. I'm not too crazy about this one, adding a get/put_cpu() in the hot path, and a cpumask test. The fact is that most/no drivers care about strict placement. We always try to do so, if convenient, since it's faster, but this seems to be doing the opposite. I'd be more inclined to have a driver flag if it needs guaranteed placement, using one an ops BLK_MQ_F_STRICT_CPU flag or similar. What do you think? -- Jens Axboe
