On Fri, 13 Jul 2012 16:38:51 +0800, Asias He <asias@xxxxxxxxxx> wrote: > Add 'virtio_blk.use_bio=1' to kernel cmdline or 'modprobe virtio_blk > use_bio=1' to enable ->make_request_fn() based I/O path. This patch conflicts with Paolo's Bonzini's 'virtio-blk: allow toggling host cache between writeback and writethrough' which is also queued (see linux-next). I'm not sure what the correct behavior for bio & cacheflush is, if any. But as to the patch itself: it's a hack. 1) Leaving the guest's admin to turn on the switch is a terrible choice. 2) The block layer should stop merging and sorting when a device is fast, not the driver. 3) I pointed out that slow disks have low IOPS, so why is this conditional? Sure, more guest exits, but it's still a small number for a slow device. 4) The only case where we want merging is on a slow device when the host isn't doing it. Now, despite this, I'm prepared to commit it. But in my mind it's a hack: we should aim for use_bio to be based on a feature bit fed from the host, and use the module parameter only if we want to override it. 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
