From mboxrd@z Thu Jan  1 00:00:00 1970
From: Anthony Liguori <anthony@codemonkey.ws>
Subject: Re: KVM performance vs. Xen
Date: Thu, 30 Apr 2009 08:45:08 -0500
Message-ID: <49F9AB64.20506@codemonkey.ws>
References: <49F8672E.5080507@linux.vnet.ibm.com> <49F967AE.4040905@redhat.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Content-Transfer-Encoding: 7bit
Cc: Andrew Theurer <habanero@linux.vnet.ibm.com>,
	kvm-devel <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
Return-path: <kvm-owner@vger.kernel.org>
Received: from qw-out-2122.google.com ([74.125.92.25]:39597 "EHLO
	qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1762098AbZD3NpN (ORCPT <rfc822;kvm@vger.kernel.org>);
	Thu, 30 Apr 2009 09:45:13 -0400
Received: by qw-out-2122.google.com with SMTP id 5so1541821qwd.37
        for <kvm@vger.kernel.org>; Thu, 30 Apr 2009 06:45:12 -0700 (PDT)
In-Reply-To: <49F967AE.4040905@redhat.com>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>

Avi Kivity wrote:
>>
>> 1) I'm seeing about 2.3% in scheduler functions [that I recognize].
>> Does that seems a bit excessive?
>
> Yes, it is.  If there is a lot of I/O, this might be due to the thread 
> pool used for I/O.

This is why I wrote the linux-aio patch.  It only reduced CPU 
consumption by about 2% although I'm not sure if that's absolute or 
relative.  Andrew?

>> 2) cpu_physical_memory_rw due to not using preadv/pwritev?
>
> I think both virtio-net and virtio-blk use memcpy().

With latest linux-2.6, and a development snapshot of glibc, virtio-blk 
will not use memcpy() anymore but virtio-net still does on the receive 
path (but not transmit).

Regards,

Anthony Liguori