From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jamie Lokier Subject: Re: [Qemu-devel] Re: [PATCH 0/4] Rework alarm timer infrastrucure - take2 Date: Sun, 19 Aug 2007 18:15:45 +0100 Message-ID: <20070819171545.GB16928@mail.shareable.org> References: <20070817231149.544849769@gmail.com> <20070819131042.GA22798@mail.shareable.org> <46C84A16.7040305@qumranet.com> <200708191457.21237.paul@codesourcery.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org, qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org, Avi Kivity To: Paul Brook Return-path: Content-Disposition: inline In-Reply-To: <200708191457.21237.paul-qD8j1LwMmJjtCj0u4l0SBw@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Paul Brook wrote: > > Yes, good thinking, but this should only be done if it actually impacts > > something. Reducing overhead from 0.1% to 0.05% is not worthwhile if it > > introduces extra complexity. > > If the overhead is that small, why are we touching this code in the first > place? Insightful. A benchmark result was posted which is rather interesting: >[mkent@localhost ~]$ time ./hackbench 50 >x86_64 host : real 0m10.845s >x86_64 host, bound to 1 cpu : real 0m21.884s >i386 guest+unix clock : real 0m49.206s >i386 guest+hpet clock : real 0m48.292s >i386 guest+dynticks clock : real 0m28.835s > >Results are repeatable and verfied with a stopwatch because I didn't >believe them at first :) I am surprised if 1000 redundant SIGALRMs per second is really causing 70% overhead in normal qemu execution, except on a rather old or slow machine where signal delivery is very slow. It would be good to understand the cause of that benchmark result. -- Jamie ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/