From mboxrd@z Thu Jan 1 00:00:00 1970 From: Uri Lublin Subject: Re: [PATCH AUTOTEST] kvm: timedrift test: fix typo (host_delta_t) Date: Thu, 04 Feb 2010 23:38:25 +0200 Message-ID: <4B6B3E51.9070701@redhat.com> References: <392923954.732161265208472656.JavaMail.root@zmail05.collab.prod.int.phx2.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: lmr@redhat.com, autotest@test.kernel.org, kvm@vger.kernel.org To: Michael Goldish Return-path: Received: from mx1.redhat.com ([209.132.183.28]:46882 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756327Ab0BDVin (ORCPT ); Thu, 4 Feb 2010 16:38:43 -0500 In-Reply-To: <392923954.732161265208472656.JavaMail.root@zmail05.collab.prod.int.phx2.redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On 02/03/2010 04:47 PM, Michael Goldish wrote: > > ----- "Uri Lublin" wrote: > >> Signed-off-by: Uri Lublin >> --- >> client/tests/kvm/tests/timedrift.py | 2 +- >> 1 files changed, 1 insertions(+), 1 deletions(-) >> >> diff --git a/client/tests/kvm/tests/timedrift.py >> b/client/tests/kvm/tests/timedrift.py >> index b3e8770..06f6a70 100644 >> --- a/client/tests/kvm/tests/timedrift.py >> +++ b/client/tests/kvm/tests/timedrift.py >> @@ -160,7 +160,7 @@ def run_timedrift(test, params, env): >> # Report results >> host_delta_total = ht2 - ht0 >> guest_delta_total = gt2 - gt0 >> - drift_total = 100.0 * (host_delta_total - guest_delta_total) / >> host_delta >> + drift_total = 100.0 * (host_delta_total - guest_delta_total) / >> host_delta_total > > This isn't a typo. > delta_total is the load duration (e.g. 1 min of video decoding) + > rest duration (e.g. 20 secs of idleness). > I think the load drift and the total drift should be divided by the > same delta, in order to determine the amount of drift corrected during > idleness. If you divide the total drift by delta_total (instead of > delta) you give a false impression that more drift was corrected than > really was. > > I'm not sure I'm making my point clearly so here's an example: > > Let's assume: > - The load duration is 30s; > - the idle duration is 30s; > - the drift was 10s; > - the drift was not corrected at all during idleness -- so after the > idle period the drift remained 10s. > > Then: > - The "load drift" is 33.3% (10/30); > - if you divide by delta, the "total drift" is still 33.3% (10/30); > - if you divide by delta_total, the "total drift" is 16.6% (10/60). > > So dividing by delta_total gives the impression that some drift was > corrected, when in fact none was. > O.K. That makes sense. Thanks for the explanation. In your example, the "total drift" is 33% of "the load duration", which is a bit confusing.