On Thu, Dec 22, 2011 at 12:57:40PM +0000, Stefan Hajnoczi wrote: > On Wed, Dec 21, 2011 at 1:00 AM, Minchan Kim <minchan@xxxxxxxxxx> wrote: > > This patch is follow-up of Christohp Hellwig's work > > [RFC: ->make_request support for virtio-blk]. > > http://thread.gmane.org/gmane.linux.kernel/1199763 > > > > Quote from hch > > "This patchset allows the virtio-blk driver to support much higher IOP > > rates which can be driven out of modern PCI-e flash devices. At this > > point it really is just a RFC due to various issues." > > Basic question to make sure I understood this series: does this patch > bypass the guest I/O scheduler (but then you added custom batching > code into virtio_blk.c)? Right. > > If you're stumped by the performance perhaps compare blktraces of the > request approach vs the bio approach. We're probably performing I/O > more CPU-efficiently but the I/O pattern itself is worse. You mean I/O scheduler have many techniques to do well in I/O pattern? That's what I want to discuss in this RFC. I guess request layer have many techniques proved during long time to do well I/O but BIO-based drvier ignores them for just reducing locking overhead. Of course, we can add such techniques to BIO-batch driver like custom-batch in this series. But it needs lots of work, is really duplication, and will have a problem on maintenance. I would like to listen opinions whether this direction is good or bad. > > Stefan -- Kind regards, Minchan Kim -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
