On 07/05/2015 12:37 PM, Christoffer Dall wrote: > 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... I think upstreaming the basic approach first (arm64, arm32 cleanups), and let this series get some good runtime - would be better and safer approach. > > Otherwise I think this sounds like a fairly good idea and I wonder if > the same could be done on arm64? Yes that's the intent, doing both architectures at once would be preferable. Thanks, Mario > > 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
