On Wed, Jul 2, 2014 at 5:49 PM, Kevin Wolf <kw...@redhat.com> wrote: > Am 02.07.2014 um 11:29 hat Ming Lei geschrieben: >> On Wed, Jul 2, 2014 at 5:12 PM, Kevin Wolf <kw...@redhat.com> wrote: >> > Am 02.07.2014 um 10:56 hat Paolo Bonzini geschrieben: >> >> Il 02/07/2014 10:39, Ming Lei ha scritto: >> >> >Then start to read payload in original path, but no plug/unplug any >> >> >more. Also another request may follows, and another plug&unplug >> >> >comes too, which makes thing more complicated, so I suggest to >> >> >enable plug&unplug only for raw driver now. >> >> >> >> That's just a performance issue (and actually one that wasn't in 2.0 >> >> because qcow2 on dataplane wasn't supported there). In many cases >> >> the cache hit of the qcow2 metadata cache can be very high, and >> >> avoiding plug/unplug would prevent an easy performance bonus. >> >> >> >> I don't especially like plug/unplug as an API (I think it's better >> >> to extend aio_multiwrite to include other kind of requests), but: >> >> >> >> - either we have qualms on the correctness of it, and then we should >> >> live with the regressions >> >> >> >> - or if the patches are not messy and reverting them is easy, we >> >> should go for it. This is what we did for dataplane in the first >> >> place, and we can keep doing it in the 2.1 dataplane code. >> > >> > Fully agree. This series is small enough and obviously fixes a >> > dataplane problem, so at least for 2.1 we should go for it. >> > >> > My thoughts in the other mail were more about where to go in the long >> > term. We need to have a decision about what API we commit to - something >> > multiwrite-like or something plug/unplug-like - before we want to start >> > converting everything to that interface. >> > >> > This is why I think we should be thinking about how to implement certain >> > optimisations (like the request merging with plug/unplug, as I mentioned; >> > or mixing read and writes in one batch with multiwrite) in both models. >> > Only when we have a reasonbly good idea of what the result would look >> > like in either case we can make an informed decision. >> >> Actually linux-aio can support to submit read/write to multi files, and >> virtio-scsi does have the use case, so in future io queue should be >> per aio-context as I posted 1st time. And I am wondering if multiwrite-like >> APIs can fit in this situation. > > Though where would you get the requests for two different files from, > within the same bdrv_plug/unplug block?
I think it is doable if io queue is per aio_context. The requests can be sent to different luns(files), see virtio_scsi_handle_cmd(). Thanks, -- Ming Lei
