Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758733AbZCRWzl (ORCPT ); Wed, 18 Mar 2009 18:55:41 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752886AbZCRWzd (ORCPT ); Wed, 18 Mar 2009 18:55:33 -0400 Received: from gw.goop.org ([64.81.55.164]:40473 "EHLO mail.goop.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752604AbZCRWzc (ORCPT ); Wed, 18 Mar 2009 18:55:32 -0400 Message-ID: <49C17BD8.6050609@goop.org> Date: Wed, 18 Mar 2009 15:55:20 -0700 From: Jeremy Fitzhardinge User-Agent: Thunderbird 2.0.0.19 (X11/20090105) MIME-Version: 1.0 To: Avi Kivity CC: Nick Piggin , Linux Kernel Mailing List , Linux Memory Management List , Xen-devel , Jan Beulich , Ingo Molnar Subject: Re: Question about x86/mm/gup.c's use of disabled interrupts References: <49C148AF.5050601@goop.org> <49C16411.2040705@redhat.com> <49C1665A.4080707@goop.org> <49C16A48.4090303@redhat.com> <49C17230.20109@goop.org> <49C17880.7080109@redhat.com> In-Reply-To: <49C17880.7080109@redhat.com> X-Enigmail-Version: 0.95.6 Content-Type: text/plain; charset=ISO-8859-1; 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: 1248 Lines: 31 Avi Kivity wrote: >> Hm, awkward if flush_tlb_others doesn't IPI... >> > > How can it avoid flushing the tlb on cpu [01]? It's it's > gup_fast()ing a pte, it may as well load it into the tlb. xen_flush_tlb_others uses a hypercall rather than an IPI, so none of the logic which depends on there being an IPI will work. >> Simplest fix is to make gup_get_pte() a pvop, but that does seem like >> putting a red flag in front of an inner-loop hotspot, or something... >> >> The per-cpu tlb-flush exclusion flag might really be the way to go. > > I don't see how it will work, without changing Xen to look at the flag? > > local_irq_disable() is used here to lock out a remote cpu, I don't see > why deferring the flush helps. Well, no, not deferring. Making xen_flush_tlb_others() spin waiting for "doing_gup" to clear on the target cpu. Or add an explicit notion of a "pte update barrier" rather than implicitly relying on the tlb IPI (which is extremely convenient when available...). J -- 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/