On Thu, 2012-03-08 at 16:47 +0100, 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. > Is that the case here? This patch might cause a mis-prediction for > non-paging guests all > the time.
Branch predictions are all about probability of occurrence, and I cannot imagine guests having paging disabled and mapping gva->gpa directly, so for most of the cases it would be beneficial. For those peculiar users that actually don't use paging, then yes, mispredictions would occur. - Davidlohr > > 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". > > > Christian > > -- 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
