From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH 0/3] Remove interrupt stack table usage from x86_64 kernel Date: Sun, 28 Dec 2008 21:34:25 +0100 Message-ID: <20081228203425.GF496@one.firstfloor.org> References: <87vdt5vfxc.fsf@basil.nowhere.org> <4956A0B1.1060908@redhat.com> <20081227224029.GB496@one.firstfloor.org> <49573FE7.9090802@redhat.com> <20081228131605.GC496@one.firstfloor.org> <49578896.8030703@redhat.com> <20081228190840.GD496@one.firstfloor.org> <4957CE78.6030706@redhat.com> <4957D14B.60805@redhat.com> <4957DCC3.3060505@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Andi Kleen , Ingo Molnar , x86@kernel.org, linux-kernel , KVM list To: Avi Kivity Return-path: Received: from one.firstfloor.org ([213.235.205.2]:56188 "EHLO one.firstfloor.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751078AbYL1UVQ (ORCPT ); Sun, 28 Dec 2008 15:21:16 -0500 Content-Disposition: inline In-Reply-To: <4957DCC3.3060505@redhat.com> Sender: kvm-owner@vger.kernel.org List-ID: On Sun, Dec 28, 2008 at 10:08:35PM +0200, Avi Kivity wrote: > Avi Kivity wrote: > >Avi Kivity wrote: > >>1. Add per-cpu IDT > > > >Or we could have just two IDTs - one with IST and one without. I > >clocked LIDT at 58 cycles (and we need two per heavyweight switch), so > >it's not that wonderful. > > This makes the whole thing unworthwhile. The vmload/vmsave pair costs > only 200 cycles (I should have started with this), and 120 cycles on the > heavyweight path plus complexity are not worth 200 cycles on the > lightweight path. Actually to switch ISTs you need to change the TSS, not the IDT. But I suppose that won't be any faster. -Andi -- ak@linux.intel.com