Hi all, here's another topic which I've hit during my performance tests: How should interrupt affinity be handled with blk-multiqueue? The problem is that the blk-multiqueue assumes a certain CPU-to-queue mapping, _and_ the 'queue' in blk-mq syntax is actually a submission/completion queue pair. To achieve optimal performance one should set the interrupt affinity for a given (hardware) queue to the matchine (blk-mq) queue. But typically the interrupt affinity has to be set during HBA setup ie way before any queues are allocated. Which means we have three choices: - outguess the blk-mq algorithm in the driver and set the interrupt affinity during HBA setup - Add some callbacks to coordinate interrupt affinity between driver and blk-mq - Defer it to manual assignment, but inferring the risk of a suboptimal performance. At LSF/MM I would like to have a discussion on how the interrupt affinity should be handled for blk-mq, and whether a generic method is possible or desirable. Also there is the issue of certain drivers (eg lpfc) which normally do interrupt affinity themselves, but disable it for multiqueue. Which results in abysmal performance when comparing single queue against multiqueue :-( As a side note, what does blk-mq do if the interrupt affinity is _deliberately_ set wrong? IE if the completions for one command arrive on completely the wrong queue? Discard the completion? Move it to the correct queue? Cheers, Hannes -- Dr. Hannes Reinecke Teamlead Storage & Networking hare@xxxxxxx +49 911 74053 688 SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton HRB 21284 (AG Nürnberg) -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
