On Tue, Dec 18, 2012 at 03:32:15PM +0100, Paolo Bonzini wrote: > Il 18/12/2012 14:59, Michael S. Tsirkin ha scritto: > >>> Can't we track state internally to the virtqueue? Exposing it > >>> seems to buy us nothing since you can't call add_buf between > >>> start and end anyway. > >> > >> I wanted to keep the state for these functions separate from the > >> rest. I don't think it makes much sense to move it to struct > >> virtqueue unless virtqueue_add_buf is converted to use the new API > >> (doesn't make much sense, could even be a tad slower). > > > > Why would it be slower? > > virtqueue_add_buf could be slower if it used the new API. That's > because of the overhead of writing and reading from struct > virtqueue_buf, instead of using variables in registers. Yes but we'll get rid of virtqueue_buf. > >> On the other hand moving it there would eliminate the dependency > >> on virtio_ring.h. Rusty, what do you think? > >> > >>> And idea: in practice virtio scsi seems to always call > >>> sg_init_one, no? So how about we pass in void* or something and > >>> avoid using sg and count? This would make it useful for -net > >>> BTW. > >> > >> It also passes the scatterlist from the LLD. It calls sg_init_one > >> for the request/response headers. > > > > Try adding a _single variant. You might see unrolling a loop gives > > more of a benefit than this whole optimization. > > Makes sense, I'll try. However, note that I *do* need the > infrastructure in this patch because virtio-scsi could never use a > hypothetical virtqueue_add_buf_single; requests always have at least 2 > buffers for the headers. > > However I could add virtqueue_add_sg_single and use it for those > headers. Right. > The I/O buffer can keep using virtqueue_add_sg. > > Paolo -- 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
