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. >> 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. 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 majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
