From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Theurer Subject: gettimeofday() vsyscall for kvm-clock? Date: Mon, 21 May 2012 15:26:54 -0500 Message-ID: <4FBAA50E.4010006@linux.vnet.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Marcelo Tosatti To: kvm@vger.kernel.org Return-path: Received: from e35.co.us.ibm.com ([32.97.110.153]:60132 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752045Ab2EUU2S (ORCPT ); Mon, 21 May 2012 16:28:18 -0400 Received: from /spool/local by e35.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 21 May 2012 14:28:18 -0600 Received: from d03relay02.boulder.ibm.com (d03relay02.boulder.ibm.com [9.17.195.227]) by d03dlp03.boulder.ibm.com (Postfix) with ESMTP id 0C1AE19D8050 for ; Mon, 21 May 2012 14:27:53 -0600 (MDT) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by d03relay02.boulder.ibm.com (8.13.8/8.13.8/NCO v10.0) with ESMTP id q4LKS4Wv196558 for ; Mon, 21 May 2012 14:28:04 -0600 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.13.1/NCO v10.0 AVout) with ESMTP id q4LKRxYw017600 for ; Mon, 21 May 2012 14:28:00 -0600 Sender: kvm-owner@vger.kernel.org List-ID: Wondering if a user-space gettimofday() for kvm-clock has been considered before. I am seeing a pretty large difference in performance between tsc and kvm-clock. I have to assume at least some of this is due to the mode switch for kvm-clock. Here are the results: (this is a 16 vCPU VM on a 16 thread 2S Nehalem-EP host, looped gettimeofday() calls on all vCPUs) tsc: .0645 usec per call kvm-clock: .4222 usec per call (6.54x) -Andrew Theurer