From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Re: [PATCH] virtio: Use ioeventfd for virtqueue notify Date: Mon, 04 Oct 2010 10:04:29 +0200 Message-ID: <4CA98A8D.4000500@redhat.com> References: <1285855312-11739-1-git-send-email-stefanha@linux.vnet.ibm.com> <4CA862A7.2080302@redhat.com> <20101003135138.GA19775@redhat.com> <4CA89185.6070302@redhat.com> <20101003142828.GB19775@redhat.com> <4CA92B79.2030805@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Steve Dobbelstein , Anthony Liguori , Stefan Hajnoczi , kvm@vger.kernel.org, "Michael S. Tsirkin" , qemu-devel@nongnu.org, Khoa Huynh , sri@linux.vnet.ibm.com To: Anthony Liguori Return-path: In-Reply-To: <4CA92B79.2030805@linux.vnet.ibm.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org Errors-To: qemu-devel-bounces+gceq-qemu-devel=gmane.org@nongnu.org List-Id: kvm.vger.kernel.org On 10/04/2010 03:18 AM, Anthony Liguori wrote: > On 10/03/2010 09:28 AM, Michael S. Tsirkin wrote: >> >>> This is using eventfd as well. >> Sorry, I meant irqfd. > > I've tried using irqfd in userspace. It hurts performance quite a bit > compared to doing an ioctl so I would suspect this too. > > A last_used_idx or similar mechanism should help performance quite a > bit on top of ioeventfd too. > Any idea why? While irqfd does quite a bit of extra locking, it shouldn't be that bad. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.