From mboxrd@z Thu Jan 1 00:00:00 1970 From: "David S. Ahern" Subject: Re: [RFC PATCH 0/3] generic hypercall support Date: Sat, 09 May 2009 22:24:59 -0600 Message-ID: <4A06571B.3020801@cisco.com> References: <4A010927.6020207@novell.com> <20090506072212.GV3036@sequoia.sous-sol.org> <4A018DF2.6010301@novell.com> <20090506160712.GW3036@sequoia.sous-sol.org> <4A031471.7000406@novell.com> <20090507233503.GA9103@amt.cnet> <20090507234311.GA9517@amt.cnet> <4A03E579.8030201@redhat.com> <20090508143507.GA8319@amt.cnet> <4A0445A0.4060104@novell.com> <20090508155109.GA9269@amt.cnet> <4A048E78.6020605@cisco.com> <4A048F93.1050601@novell.com> <4A04BEE5.2080600@cisco.com> <4A054296.4070604@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: Gregory Haskins , Marcelo Tosatti , Chris Wright , Gregory Haskins , kvm@vger.kernel.org, Anthony Liguori To: Avi Kivity Return-path: Received: from sj-iport-5.cisco.com ([171.68.10.87]:34195 "EHLO sj-iport-5.cisco.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750743AbZEJEZA (ORCPT ); Sun, 10 May 2009 00:25:00 -0400 In-Reply-To: <4A054296.4070604@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: Avi Kivity wrote: > David S. Ahern wrote: >> I ran another test case with SMT disabled, and while I was at it >> converted TSC delta to operations/sec. The results without SMT are >> confusing -- to me anyways. I'm hoping someone can explain it. >> Basically, using a count of 10,000,000 (per your web page) with SMT >> disabled the guest detected a soft lockup on the CPU. So, I dropped the >> count down to 1,000,000. So, for 1e6 iterations: >> >> without SMT, with EPT: >> HC: 259,455 ops/sec >> PIO: 226,937 ops/sec >> MMIO: 113,180 ops/sec >> >> without SMT, without EPT: >> HC: 274,825 ops/sec >> PIO: 247,910 ops/sec >> MMIO: 111,535 ops/sec >> >> Converting the prior TSC deltas: >> >> with SMT, with EPT: >> HC: 994,655 ops/sec >> PIO: 875,116 ops/sec >> MMIO: 439,738 ops/sec >> >> with SMT, without EPT: >> HC: 994,304 ops/sec >> PIO: 903,057 ops/sec >> MMIO: 423,244 ops/sec >> >> Running the tests repeatedly I did notice a fair variability (as much as >> -10% down from these numbers). >> >> Also, just to make sure I converted the delta to ops/sec, the formula I >> used was cpu_freq / dTSC * count = operations/sec >> >> > > The only think I can think of is cpu frequency scaling lying about the > cpu frequency. Really the test needs to use time and not the time stamp > counter. > > Are the results expressed in cycles/op more reasonable? > Power settings seem to be the root cause. With this HP server the SMT mode must be disabling or overriding a power setting that is enabled in the bios. I found one power-based knob that gets non-SMT performance close to SMT numbers. Not very intuitive that SMT/non-SMT can differ so dramatically. david