From mboxrd@z Thu Jan 1 00:00:00 1970 From: Martin Mailand Subject: Re: virtio-blk performance regression and qemu-kvm Date: Tue, 28 Feb 2012 17:39:54 +0100 Message-ID: <4F4D035A.60107@tuxadero.com> References: <20120210143639.GA17883@gmail.com> <20120221155725.GA950@gmail.com> <20120222164840.GA8517@gmail.com> Reply-To: martin@tuxadero.com Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Dongsu Park , qemu-devel@nongnu.org, kvm@vger.kernel.org To: Stefan Hajnoczi Return-path: Received: from einhorn.in-berlin.de ([192.109.42.8]:45231 "EHLO einhorn.in-berlin.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S964813Ab2B1QkG (ORCPT ); Tue, 28 Feb 2012 11:40:06 -0500 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: Hi, I could reproduce it and I bisected it down to this commit. 12d4536f7d911b6d87a766ad7300482ea663cea2 is the first bad commit commit 12d4536f7d911b6d87a766ad7300482ea663cea2 Author: Anthony Liguori Date: Mon Aug 22 08:24:58 2011 -0500 -martin On 22.02.2012 20:53, Stefan Hajnoczi wrote: > On Wed, Feb 22, 2012 at 4:48 PM, Dongsu Park > wrote: >>> Try turning ioeventfd off for the virtio-blk device: >>> >>> -device virtio-blk-pci,ioeventfd=off,... >>> >>> You might see better performance since ramdisk I/O should be very >>> low-latency. The overhead of using ioeventfd might not make it >>> worthwhile. The ioeventfd feature was added post-0.14 IIRC. Normally >>> it helps avoid stealing vcpu time and also causing lock contention >>> inside the guest - but if host I/O latency is extremely low it might >>> be faster to issue I/O from the vcpu thread. >> Thanks for the tip. I tried that too, but no success. > My guesses have all been wrong. Maybe it's time to git bisect this instead :). > > Stefan > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([208.118.235.92]:33803) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2QQW-0002M9-Ll for qemu-devel@nongnu.org; Tue, 28 Feb 2012 12:01:31 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1S2QQR-0000wo-K5 for qemu-devel@nongnu.org; Tue, 28 Feb 2012 12:01:24 -0500 Received: from einhorn.in-berlin.de ([192.109.42.8]:45461) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1S2QQR-0000wD-AQ for qemu-devel@nongnu.org; Tue, 28 Feb 2012 12:01:19 -0500 Message-ID: <4F4D035A.60107@tuxadero.com> Date: Tue, 28 Feb 2012 17:39:54 +0100 From: Martin Mailand MIME-Version: 1.0 References: <20120210143639.GA17883@gmail.com> <20120221155725.GA950@gmail.com> <20120222164840.GA8517@gmail.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] virtio-blk performance regression and qemu-kvm Reply-To: martin@tuxadero.com List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Dongsu Park , kvm@vger.kernel.org, qemu-devel@nongnu.org Hi, I could reproduce it and I bisected it down to this commit. 12d4536f7d911b6d87a766ad7300482ea663cea2 is the first bad commit commit 12d4536f7d911b6d87a766ad7300482ea663cea2 Author: Anthony Liguori Date: Mon Aug 22 08:24:58 2011 -0500 -martin On 22.02.2012 20:53, Stefan Hajnoczi wrote: > On Wed, Feb 22, 2012 at 4:48 PM, Dongsu Park > wrote: >>> Try turning ioeventfd off for the virtio-blk device: >>> >>> -device virtio-blk-pci,ioeventfd=off,... >>> >>> You might see better performance since ramdisk I/O should be very >>> low-latency. The overhead of using ioeventfd might not make it >>> worthwhile. The ioeventfd feature was added post-0.14 IIRC. Normally >>> it helps avoid stealing vcpu time and also causing lock contention >>> inside the guest - but if host I/O latency is extremely low it might >>> be faster to issue I/O from the vcpu thread. >> Thanks for the tip. I tried that too, but no success. > My guesses have all been wrong. Maybe it's time to git bisect this instead :). > > Stefan > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html