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" [off-list ref] wrote:

quoted

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?

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 :)