On Mon, Oct 28, 2013 at 01:17:54PM +1030, Rusty Russell wrote: > Let's pretend I'm stupid. > > We don't actually have multiple queues through to the host, but we're > pretending to, because it makes the block layer go faster? > > Do I want to know *why* it's faster? Or should I look the other way?
You shouldn't. To how multiple queues benefit here I'd like to defer to Jens, given the single workqueue I don't really know where to look here. The real benefit that unfortunately wasn't obvious from the description is that even with just a single queue the blk-multiqueue infrastructure will be a lot faster, because it is designed in a much more streaminline fashion and avoids lots of lock roundtrips both during submission itself and for submission vs complettion. Back when I tried to get virtio-blk to perform well on high-end flash (the work that Asias took over later) the queue_lock contention was the major issue in virtio-blk and this patch gets rid of that even with a single queue. A good example are the patches from Nick to move scsi drivers over to the infrastructure that only support a single queue. Even that gave over a 10 fold improvement over the old code. Unfortunately I do not have access to this kind of hardware at the moment, but I'd love to see if Asias or anyone at Red Hat could redo those old numbers. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
