From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH] x86/hvm: accelerate IO intercept handling Date: Fri, 05 Mar 2010 14:52:02 +0000 Message-ID: References: <4B91170A.2060601@amd.com> Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <4B91170A.2060601@amd.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: Andre Przywara Cc: xen-devel List-Id: xen-devel@lists.xenproject.org On 05/03/2010 14:36, "Andre Przywara" wrote: > I simply boot tested both versions and ran some simple benchmarks. > A micro benchmark (hammering an I/O port in a tight loop) shows a > significant performance improvement (down to 66% of the time needed to > handle the intercept on a K8, measured in the guest with TSC). > Even with reading a 1GB file from an emulated IDE harddisk (Dom0 cached) > I could get a 4-5% improvement. > We found some guests (e.g. the TCP stack in some Windows version) which > exercise the PM-Timer I/O port (0x1F48) very often (multiple 10,000 > times per second), these workloads also benefit from this patch. By how much? I mean, the microbenchmark and 5% speedup on our poor-man's IO path are not very interesting. Unless the speedup on the only possibly-interesting workload you mention is significant, this whole optimisation seems unnecessary. -- Keir