On Mon, 2012-03-12 at 14:12 +0200, Avi Kivity wrote: > On 03/08/2012 05:47 PM, Christian Borntraeger wrote: > > On 08/03/12 12:45, Davidlohr Bueso wrote: > > > From: Davidlohr Bueso <[email protected]> > > > > > > Since most guests will have paging enabled for memory management, add > > > likely() optimization > > > around CR0.PG checks. > > > > > { > > > - return kvm_read_cr0_bits(vcpu, X86_CR0_PG); > > > + return likely(kvm_read_cr0_bits(vcpu, X86_CR0_PG)); > > > > > > IMHO likely/unlikely should be considered more as fast-path/slow-path and > > not as often/less often. > > Agree. > > > Is that the case here? This patch might cause a mis-prediction for > > non-paging guests all > > the time. > > > > Non-paging might be really irrelevant, so I am just making a point, since > > likely/unlikely is mis-used too often especially for "most users do it that > > way". > > In fact this is a classic example. Almost no guests use real mode (the > last guests to use real mode extensively was DOS; I think Win9x switches > to real mode pretty often). As it's a user-controlled setting, we're > penalizing users who do things differently. > > However the majority if is_paging() == true guests is so huge, and since > non-paging guests don't really expect 2012 performance levels anyway > (being so old) that I think in practice this is a good optimization here.
Avi, will you be taking this patch? I don't see it applied or for pull in 3.4. Thanks. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
