Hi Mario, On Wed, Jun 24, 2015 at 08:30:25PM -0700, Mario Smarduch wrote: > Currently we do a lazy VFP switch in Hyp mode, but once we exit and re-enter hyp > mode we trap again on VFP access. This mode has shown around 30-50% improvement > running hackbench and lmbench. > > This patch series extends lazy VFP switch beyond Hyp mode to KVM host mode. > > 1 - On guest access we switch from host to guest and set a flag accessible to > host > 2 - On exit to KVM host, VFP state is restored on vcpu_put if flag is marked (1) > 3 - Otherwise guest is resumed and continues to use its VFP registers. > 4 - In case of 2 on VM entry we set VFP trap flag to repeat 1. > > If guest does not access VFP registers them implemenation remains the same. > > Executing hackbench on Fast Models and Exynos arm32 board shows good > results. Considering all exits 2% of the time KVM host lazy vfp switch is > invoked. > > Howeverr this patch set requires more burn in time and testing under various > loads. > > Currently ARM32 is addressed later ARM64. > I think Marc said that he experimented with a similar patch once, but that it caused corruption on the host side somehow. Am I remembering correctly? If so, we would need to make sure this doesn't happen with this patch set... Otherwise I think this sounds like a fairly good idea and I wonder if the same could be done on arm64? Thanks, -Christoffer -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
