From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Jan Beulich" Subject: Re: [PATCH, RFC] i386: highmem access assistance hypercalls Date: Mon, 20 Oct 2008 14:40:51 +0100 Message-ID: <48FCA683.76E4.0078.0@novell.com> References: <48F8CB2D.76E4.0078.0@novell.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <48F8CB2D.76E4.0078.0@novell.com> Content-Disposition: inline List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org >>> "Jan Beulich" 17.10.08 17:28 >>> >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. Actually, the workload I used for measuring the effect on page copying was not meaningful. On an (artificial) workload that really exercises page copying in a meaningful way, the improvement is about 15%. Also, the improvements on a 64-bit hypervisor are, as expected, even a little better (close to 25% for page clearing and close to 20% for page copying - with the original numbers already having been slightly better than on a 32-bit hypervisor). Jan