Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752488Ab1BHJQE (ORCPT ); Tue, 8 Feb 2011 04:16:04 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51004 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751253Ab1BHJQB (ORCPT ); Tue, 8 Feb 2011 04:16:01 -0500 Message-ID: <4D5109CC.2030901@redhat.com> Date: Tue, 08 Feb 2011 11:15:56 +0200 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.2.13) Gecko/20101209 Fedora/3.1.7-0.35.b3pre.fc14 Lightning/1.0b3pre Thunderbird/3.1.7 MIME-Version: 1.0 To: Jan Kiszka CC: Zachary Amsden , Marcelo Tosatti , kvm , Linux Kernel Mailing List Subject: Re: [PATCH] KVM: x86: Convert tsc_write_lock to raw_spinlock References: <4D4BCB97.6000900@siemens.com> <4D4C698A.4010201@redhat.com> <4D4FD8EE.6040009@siemens.com> <4D4FFD97.6010805@redhat.com> <4D5008F0.5060200@siemens.com> <4D500C9F.2080501@redhat.com> <4D50120F.4030809@siemens.com> <4D501547.6040907@redhat.com> <4D501698.1000507@siemens.com> <4D501D43.5060608@redhat.com> <4D5024F3.9090105@siemens.com> <4D5027A1.8000505@redhat.com> <4D502AA5.7040407@siemens.com> In-Reply-To: <4D502AA5.7040407@siemens.com> Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1761 Lines: 45 On 02/07/2011 07:23 PM, Jan Kiszka wrote: > On 2011-02-07 18:10, Avi Kivity wrote: > > On 02/07/2011 06:59 PM, Jan Kiszka wrote: > >>> > >>> (well, actually, cpufreq_notifier and kvm_arch_hardware_enable are > >>> already non preemptible, and the stats code should just go away?) > >> > >> The stats code is trivial to convert, so it doesn't matter. > > > > Removal is easier. > > Is that stat interface no longer used? It's there for compatibility. I'm itching to remove it. See qemu-kvm.git/kvm/kvm_stat for the only known user, and for the replacement via tracepoints. Tracepoints have marginally lower overhead when disabled, and somewhat higher overhead when enabled. A disadvantage of tracepoints is that it is harder to associate an event with a vm when that event is triggered by a workqueue, but I don't think it matters in practice (kvm_stat doesn't even provide a per-vm breakdown). > > > >> But what about mmu_shrink and its list_move_tail? How is this > >> synchronized against kvm_destroy_vm - already today? > > > > kvm_destroy_vm() takes kvm_lock. If a vm is destroyed before > > mmu_shrink(), mmu_shrink() will never see it. If we reach mmu_shrink() > > before kvm_destroy_vm(), the latter will wait until mmu_shrink() is done. > > > > Ah, I was confused. Would require some more logic if we wanted to make > the loop lock-less, though. Yes, the usual rcu_read_lock() / grab reference / rcu_read_unlock(). -- error compiling committee.c: too many arguments to function -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/