From mboxrd@z Thu Jan 1 00:00:00 1970 From: Gianluca Guida Subject: Re: vnif socket buffer mistaken for pagetable page causes major performance problem Date: Tue, 09 Jun 2009 14:25:54 +0100 Message-ID: <4A2E62E2.7030500@eu.citrix.com> References: <2ee9aac0-0772-4306-a9e5-bf711cf2c2d8@default> <4A2CD5B3.4090700@eu.citrix.com> <4A2D3AB2.5020104@oracle.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4A2D3AB2.5020104@oracle.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Herbert van den Bergh Cc: Dan Magenheimer , "Xen-Devel (E-mail)" List-Id: xen-devel@lists.xenproject.org Herbert van den Bergh wrote: >> Can you be a little more specific about what is the performance loss, > Network throughput was reduced to 10% of normal. >> in what workload, > A network send throughput test using netperf. This is with a Linux guest (HVM of course), right? >> and what heuristic you found to be wrong in this case? > The access pattern to the memory page that was recognized as a pagetable > access was a regular memcpy doing 4 byte aligned writes into a newly > allocated page. I'm not that familiar with the shadow pagetable code, > so I don't know how "wrong" this is, just that it caused a false > positive on this type of memory access. Most probably the guest OS is recycling a page that used to be a pagetable and that is still shadowed. Thanks, Gianluca