From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932298Ab1IHHxg (ORCPT ); Thu, 8 Sep 2011 03:53:36 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41071 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932243Ab1IHHxe (ORCPT ); Thu, 8 Sep 2011 03:53:34 -0400 Message-ID: <4E6873FE.3040603@redhat.com> Date: Thu, 08 Sep 2011 10:51:26 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:6.0) Gecko/20110816 Thunderbird/6.0 MIME-Version: 1.0 To: Jeremy Fitzhardinge CC: Don Zickus , Peter Zijlstra , "H. Peter Anvin" , Linus Torvalds , Ingo Molnar , the arch/x86 maintainers , Linux Kernel Mailing List , Nick Piggin , Marcelo Tosatti , KVM , Andi Kleen , Xen Devel , Jeremy Fitzhardinge , Stefano Stabellini Subject: Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking References: <1314996468.8255.0.camel@twins> <4E614FBD.2030509@goop.org> <20110906151408.GA7459@redhat.com> <4E66615E.8070806@goop.org> <20110906182758.GR5795@redhat.com> <4E66EF86.9070200@redhat.com> <20110907134411.GV5795@redhat.com> <4E678992.5050709@redhat.com> <20110907155657.GX5795@redhat.com> <4E679AF4.50209@redhat.com> <20110907165203.GQ6838@redhat.com> <4E67A551.4000502@redhat.com> <4E67A71A.5070903@goop.org> <4E67ACB6.40107@redhat.com> <4E67C15B.3000408@goop.org> In-Reply-To: <4E67C15B.3000408@goop.org> 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 On 09/07/2011 10:09 PM, Jeremy Fitzhardinge wrote: > On 09/07/2011 10:41 AM, Avi Kivity wrote: > >> Hm, I'm interested to know what you're thinking in more detail. Can you > >> leave an NMI pending before you block in the same way you can with > >> "sti;halt" with normal interrupts? > > > > > > Nope. But you can do > > > > if (regs->rip in critical section) > > regs->rip = after_halt; > > > > and effectively emulate it. The critical section is something like > > > > critical_section_start: > > if (woken_up) > > goto critical_section_end; > > hlt > > critical_section_end: > > Hm. It's a pity you have to deliver an actual interrupt to implement > the kick though. I don't think it's that expensive, especially compared to the double-context-switch and vmexit of the spinner going to sleep. On AMD we do have to take an extra vmexit (on IRET) though. > >> > >> I was thinking you might want to do something with monitor/mwait to > >> implement the blocking/kick ops. (Handwave) > >> > > > > monitor/mwait are incredibly expensive to virtualize since they > > require write-protecting a page, IPIs flying everywhere and flushing > > tlbs, not to mention my lovely hugepages being broken up mercilessly. > > Or what about a futex-like hypercall? > Well we could have a specialized sleep/wakeup hypercall pair like Xen, but I'd like to avoid it if at all possible. -- I have a truly marvellous patch that fixes the bug which this signature is too narrow to contain.