From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: Slowdowns comparing qemu-kvm.git to qemu.git: vcpu/thread scheduling differences Date: Mon, 08 Feb 2010 08:57:05 -0600 Message-ID: <4B702641.5060907@codemonkey.ws> References: <20100208134645.GA19130@amit-x200.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: KVM List , qemu-devel@nongnu.org, Marcelo Tosatti To: Amit Shah Return-path: Received: from mail-iw0-f182.google.com ([209.85.223.182]:40393 "EHLO mail-iw0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750804Ab0BHO5J (ORCPT ); Mon, 8 Feb 2010 09:57:09 -0500 Received: by iwn12 with SMTP id 12so7125378iwn.26 for ; Mon, 08 Feb 2010 06:57:07 -0800 (PST) In-Reply-To: <20100208134645.GA19130@amit-x200.redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02/08/2010 07:46 AM, Amit Shah wrote: > Hello, > > In my testing of virtio-console, I found qemu-kvm.git introduces a lot > of overhead in thread scheduling compared to qemu.git. > > My test sends a 260M file from the host to a guest via a virtio-console > port and then computes the sha1sum of the file on the host as well as on > the guest, compares the checksum and declares the result based on the > checksum match. The test passes in all the scenarios listed below, > indicating there's no unsafe data transfer. > > > Repo Time taken > ----- ---------- > qemu.git< 1 m (typically 30s) > qemu-kvm.git> 16m > qemu-iothread ~ 5m > That very likely suggests that there are missing qemu_notify_events() in qemu-kvm.git and you're getting blocked waiting for the next timer event to fire. IOW, I assume that during the qemu-kvm.git run, the CPU isn't pegged at 100% whereas it is in qemu.git. Regards, Anthony Liguori