On Fri, Jun 04, 2010 at 08:46:49PM +0930, Rusty Russell wrote: > On Fri, 4 Jun 2010 08:05:43 pm Michael S. Tsirkin wrote: > > On Fri, Jun 04, 2010 at 12:04:57PM +0930, Rusty Russell wrote: > > > On Wed, 2 Jun 2010 12:17:12 am Michael S. Tsirkin wrote: > > > > This adds an (unused) option to put available ring before control (avail > > > > index, flags), and adds padding between index and flags. This avoids > > > > cache line sharing between control and ring, and also makes it possible > > > > to extend avail control without incurring extra cache misses. > > > > > > > > Signed-off-by: Michael S. Tsirkin <m...@redhat.com> > > > > > > No no no no. 254? You're trying to Morton me![1] > > > > Hmm, I wonder what will we do if we want a 3rd field on > > a separate chacheline. But ok. > > > > > How's this (untested): > > > > I think we also want to put flags there as well, > > they are used on interrupt path, together with last used index. > > I'm uncomfortable with moving a field. > > We haven't done that before and I wonder what will break with old code.
With e.g. my patch, We only do this conditionally when bit is negotitated. > Should we instead just abandon the flags field and use last_used only? > Or, more radically, put flags == last_used when the feature is on? > > Thoughts? > Rusty. Hmm, e.g. with TX and virtio net, we almost never want interrupts, whatever the index value. -- MST
