On Wed, 2014-02-26 at 16:49 +0100, Paolo Bonzini wrote: > Alex Williamson reported that a Windows game does something weird that > makes the guest save and restore debug registers on each context switch. > This cause several hundred thousands vmexits per second, and basically > cuts performance in half when running under KVM. > > However, when not running in guest-debug mode, the guest controls the > debug registers and having to take an exit for each DR access is a waste > of time. We just need one vmexit to load any stale values of DR0-DR6, > and then we can let the guest run freely. On the next vmexit (whatever > the reason) we will read out whatever changes the guest made to the > debug registers. > > On top of this, we can implement SVM support and let nested guests run > with dirty debug registers too. > > Paolo Bonzini (4): > KVM: vmx: we do rely on loading DR7 on entry > KVM: x86: change vcpu->arch.switch_db_regs to a bit mask > KVM: x86: Allow the guest to run with dirty debug registers > KVM: vmx: Allow the guest to run with dirty debug registers > > arch/x86/include/asm/kvm_host.h | 8 ++++++- > arch/x86/kvm/vmx.c | 48 +++++++++++++++++++++++++++++++++++++---- > arch/x86/kvm/x86.c | 29 +++++++++++++++++++++++-- > 3 files changed, 78 insertions(+), 7 deletions(-) > I see a slightly better than 100% improvement in the frame rate in Borderlands2 running in a VM with assigned Nvidia GPU with this series. Tested-by: Alex Williamson <alex.williamson@xxxxxxxxxx> -- 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
