On Sun, 29 Jul 2012 14:11:15 +0300, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > On Sat, Jul 28, 2012 at 10:21:05AM +0800, Asias He wrote: > > This patch introduces bio-based IO path for virtio-blk. > > > > Compared to request-based IO path, bio-based IO path uses driver > > provided ->make_request_fn() method to bypasses the IO scheduler. It > > handles the bio to device directly without allocating a request in block > > layer. This reduces the IO path in guest kernel to achieve high IOPS > > and lower latency. The downside is that guest can not use the IO > > scheduler to merge and sort requests. However, this is not a big problem > > if the backend disk in host side uses faster disk device. > > If this optimization depends on the host, then it > should be reported to the guest using a feature bit, > as opposed to being guest driven. I consider this approach a half-way step. Quick attempts on my laptop and I couldn't find a case where the bio path was a loss, but in theory if the host wasn't doing any reordering and it was a slow device, you'd want the guest to do so. I'm not sure if current qemu can be configured to do such a thing? Cheers, Rusty. -- 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
