From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: Paravirt KVM capabilities Date: Wed, 10 Jan 2007 20:12:27 +0200 Message-ID: <45A52C8B.70608@qumranet.com> References: <20070109141916.GA13276@vlad.carfax.org.uk> <45A3A642.1030604@qumranet.com> <1168384852.19646.161.camel@localhost.localdomain> <20070110094750.GA934@elte.hu> <45A4BB74.9010102@redhat.com> <20070110101839.GA6444@elte.hu> <45A4C345.5050404@qumranet.com> <20070110105202.GA13412@elte.hu> <45A4C7ED.8090003@qumranet.com> <20070110111442.GA16867@elte.hu> <45A529DB.4030009@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Return-path: To: Ulrich Drepper In-Reply-To: <45A529DB.4030009-H+wXaHxf7aLQT0dZR+AlfA@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 Ulrich Drepper wrote: > Ingo Molnar wrote: > >> that alone is already ~100-200 cycles overhead, it essentially doubles >> the null syscall overhead. It matters at millions of syscalls per second >> workloads, 100 cycles overhead at 1 million syscalls a second means 5% >> performance difference at 2GHz. >> > > Plus, x86-64 uses only syscall which doesn't have the opportunity to be > intercepted in ring 1, right? That's the much more important target > going forward. > Agreed. 64-bit syscalls are much better with hardware assist. [Everyone complains how x86 is loaded with 20+ years of cruft; AMD comes and cleans it up; then we discover how 4 rings and segmentation are actually useful] [[Can't a paravirtualized kernel use a vdso to use int $0x80 instead of syscall?]] -- Do not meddle in the internals of kernels, for they are subtle and quick to panic. ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys - and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV