From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail191.messagelabs.com (mail191.messagelabs.com [216.82.242.19]) by kanga.kvack.org (Postfix) with ESMTP id 1D6956B003D for ; Wed, 18 Mar 2009 18:55:33 -0400 (EDT) Message-ID: <49C17BD8.6050609@goop.org> Date: Wed, 18 Mar 2009 15:55:20 -0700 From: Jeremy Fitzhardinge MIME-Version: 1.0 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> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Avi Kivity Cc: Nick Piggin , Linux Kernel Mailing List , Linux Memory Management List , Xen-devel , Jan Beulich , Ingo Molnar List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org