From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeremy Fitzhardinge Subject: Re: [PATCH, RFC] i386: highmem access assistance hypercalls Date: Fri, 24 Oct 2008 17:01:36 -0700 Message-ID: <490261E0.8020007@goop.org> References: <48F8CB2D.76E4.0078.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <48F8CB2D.76E4.0078.0@novell.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: Jan Beulich Cc: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org Jan Beulich wrote: > While looking at the origin of very frequently executed hypercalls I > realized that the high page accessor functions in Linux would be good > candidates to handle in the hypervisor - clearing or copying to/from > a high page is a pretty frequent operation (provided there's enough > memory in the domain). While prior to the first submission I only > measured kernel builds (where the results are not hinting at a > meaningful improvement), I now found time to do a more specific > analysis: page clearing is being improved by about 20%, page copying > doesn't seem to significantly benefit (though that may be an effect of > the simplistic copy_page() implementation Xen currently uses) - > nevertheless I would think that if one function is supported by the > hypervisor, then the other should also be. > > The hypervisor patch is below (using temporary numbers for the newly > added sub-hypercalls), the Linux patch didn't change over the first > submission (if the patch here is acceptable, I'll create a version > that applies to the 2.6.18 tree). > > Opinions? > Do you have any thoughts about what it would take to make this be useful in a pvops kernel? If the Novell kernel is the only user, it seems like a bit of a dead end. J