Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754237Ab1BGQ7q (ORCPT ); Mon, 7 Feb 2011 11:59:46 -0500 Received: from thoth.sbs.de ([192.35.17.2]:29734 "EHLO thoth.sbs.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753880Ab1BGQ7p (ORCPT ); Mon, 7 Feb 2011 11:59:45 -0500 Message-ID: <4D5024F3.9090105@siemens.com> Date: Mon, 07 Feb 2011 17:59:31 +0100 From: Jan Kiszka User-Agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 MIME-Version: 1.0 To: Avi Kivity 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> In-Reply-To: <4D501D43.5060608@redhat.com> Content-Type: text/plain; charset=ISO-8859-15 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1657 Lines: 42 On 2011-02-07 17:26, Avi Kivity wrote: > On 02/07/2011 05:58 PM, Jan Kiszka wrote: >> On 2011-02-07 16:52, Avi Kivity wrote: >>> On 02/07/2011 05:38 PM, Jan Kiszka wrote: >>>>> >>>>> I don't know as it is allowed to sleep, it doesn't call any sleeping >>>>> functions to my knowledge. What worries me in the RT case is that the >>>>> spinlock acquired for hardware_enable might be preempted and run on >>>>> another CPU, which obviously isn't what you want. >>>> >>>> I see now, there are calls to raw_smp_processor_id. >>>> >>>> I think it's best to make this a raw lock. At this chance, some >>>> read-only users of vm_list should be rcu'ified. Will have a look. >>> >>> vm_list is rarely used, for either read or write. I don't see the need >>> to rcu it. >> >> Avoid that code under this lock expands the preempt-disabled period, >> specifically under -rt, and specifically as the number of objects over >> which we loop is user-defined. > > Good point; even under non-rt. > > (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. But what about mmu_shrink and its list_move_tail? How is this synchronized against kvm_destroy_vm - already today? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux -- 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/