Re: [PATCH v7 16/46] virtio_blk: v1.0 support

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Dec 01, 2014 at 01:02:58PM +0100, Cornelia Huck wrote:
> On Mon, 1 Dec 2014 13:46:45 +0200
> "Michael S. Tsirkin" <mst@redhat.com> wrote:
> 
> > On Mon, Dec 01, 2014 at 12:33:15PM +0100, Cornelia Huck wrote:
> > > On Mon, 1 Dec 2014 11:26:58 +0200
> > > "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > > 
> > > > For some places on data path, it might be worth it
> > > > to cache the correct value e.g. as part of device
> > > > structure. This replaces a branch with a memory load,
> > > > so the gain would have to be measured, best done
> > > > separately?
> > > 
> > > I think we'll want to do some measuring once the basic structure is
> > > in place anyway.
> > 
> > What's meant by in place here?
> 
> That this patchset is ready :)

Also it's ready to the level where benchmarking is possible, right?  I
don't think you should wait until we finish polishing up commit
messages.

> > 
> > > We should make sure that e.g. s390 only takes minor
> > > hit due to all that swapping that is needed for standard-compliant
> > > devices. Caching the value might certainly help in some paths.
> > 
> > Well, this is queued in linux-next for 3.19, so
> > now's the time to do it :)
> 
> So much to do, so little time...
> 
> I'm still feeling a bit uncomfortable with some of the changes
> (virtio-scsi etc.) as I have not been able to test them yet (as there's
> no converted qemu for these yet). The virtio-net and virtio-blk changes
> seem sane, though, and virtio-ccw should be fine as well.
> 
> OTOH, it's not like we're introducing new external interfaces, so later
> rework should be fine.