From mboxrd@z Thu Jan 1 00:00:00 1970 From: Paul Mackerras Subject: Re: [PATCH] KVM: PPC: Book3S HV: Optimise mmio emulation for devices on FAST_MMIO_BUS Date: Fri, 22 Feb 2019 20:39:02 +1100 Message-ID: <20190222093902.GB6006@blackberry> References: <20190207045650.18322-1-sjitindarsingh@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: linuxppc-dev@lists.ozlabs.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org To: Suraj Jitindar Singh Return-path: Content-Disposition: inline In-Reply-To: <20190207045650.18322-1-sjitindarsingh@gmail.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+glppe-linuxppc-embedded-2=m.gmane.org@lists.ozlabs.org Sender: "Linuxppc-dev" List-Id: kvm.vger.kernel.org On Thu, Feb 07, 2019 at 03:56:50PM +1100, Suraj Jitindar Singh wrote: > Devices on the KVM_FAST_MMIO_BUS by definition have length zero and are > thus used for notification purposes rather than data transfer. For > example eventfd for virtio devices. > > This means that when emulating mmio instructions which target devices on > this bus we can immediately handle them and return without needing to load > the instruction from guest memory. > > For now we restrict this to stores as this is the only use case at > present. > > For a normal guest the effect is negligible, however for a nested guest > we save on the order of 5us per access. > > Signed-off-by: Suraj Jitindar Singh Thanks, applied to my kvm-ppc-next tree. Paul.