From mboxrd@z Thu Jan 1 00:00:00 1970 From: Juergen Gross Subject: Re: Poor HVM performance with 8 vcpus Date: Wed, 14 Oct 2009 11:17:07 +0200 Message-ID: <4AD59713.3090205@ts.fujitsu.com> References: <4ACC3B49.4060500@ts.fujitsu.com> <4ACD907F.7030505@ts.fujitsu.com> <4AD588D9.4040104@ts.fujitsu.com> <20091014084147.GG20579@whitby.uk.xensource.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20091014084147.GG20579@whitby.uk.xensource.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: Tim Deegan Cc: Gianluca Guida , "xen-devel@lists.xensource.com" List-Id: xen-devel@lists.xenproject.org Tim Deegan wrote: > At 09:16 +0100 on 14 Oct (1255511785), Juergen Gross wrote: >> as the performance of BS2000 seems to be hit by OOS optimization, I'm >> thinking of making a patch to disable this feature by a domain parameter. >> >> Is there a way to do this without having to change all places where the >> #if statements are placed? >> I think there should be some central routines where adding an "if" could >> be enough (setting oos_active to 0 seems not to be enough, I fear). >> >> Do you have any hint? > > The simplest way is to cause sh_unsync() to immediately return 0. That > won't be quite as fast as #defining it all away but will avoid the > expensive paths that cause lock contention. You can add your flag to > the big if statement that's already there to avoid unsafe cases. Thanks, I'll try. > > Incidentally, although your benchmark does poorly on 8 VCPUs it might be > worth trying a less aggressively targeted benchmark -- we found on > Windows VMs that more realistic tests (e.g. Sysmark) still showed a > slight improvement from the OOS optimization at 8 vcpus. The benchmark is designed to be a realistic simulation of a typical customer batch load. Many BS2000 customers would see similar performance effects. Juergen -- Juergen Gross Principal Developer Operating Systems TSP ES&S SWE OS6 Telephone: +49 (0) 89 636 47950 Fujitsu Technolgy Solutions e-mail: juergen.gross@ts.fujitsu.com Otto-Hahn-Ring 6 Internet: ts.fujitsu.com D-81739 Muenchen Company details: ts.fujitsu.com/imprint.html