From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751842AbdBMWeO convert rfc822-to-8bit (ORCPT ); Mon, 13 Feb 2017 17:34:14 -0500 Received: from mx1.redhat.com ([209.132.183.28]:36352 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751501AbdBMWeL (ORCPT ); Mon, 13 Feb 2017 17:34:11 -0500 Subject: Re: [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function To: Peter Zijlstra References: <1486741389-8513-1-git-send-email-longman@redhat.com> <20170210161928.GI6515@twins.programming.kicks-ass.net> <1c949ed0-1b88-ae6e-4e6c-426502bfab5f@redhat.com> <14854496-0baa-1bf6-c819-f3d7fae13c2c@redhat.com> <20170213104716.GM6515@twins.programming.kicks-ass.net> <20170213105343.GJ6536@twins.programming.kicks-ass.net> <3dc50409-60dd-ad47-f971-448191e66038@redhat.com> <6f69b112-7ae4-bf8f-b767-29a68fd48632@redhat.com> <20170213215220.GN25813@worktop.programming.kicks-ass.net> Cc: Jeremy Fitzhardinge , Chris Wright , Alok Kataria , Rusty Russell , Ingo Molnar , Thomas Gleixner , "H. Peter Anvin" , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Pan Xinhui , Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Boris Ostrovsky , Juergen Gross From: Waiman Long Organization: Red Hat Message-ID: <933ba8c6-4ebe-63e2-3c3a-2e5afef9269a@redhat.com> Date: Mon, 13 Feb 2017 17:34:01 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20170213215220.GN25813@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8BIT X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.28]); Mon, 13 Feb 2017 22:34:06 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 02/13/2017 04:52 PM, Peter Zijlstra wrote: > On Mon, Feb 13, 2017 at 03:12:45PM -0500, Waiman Long wrote: >> On 02/13/2017 02:42 PM, Waiman Long wrote: >>> On 02/13/2017 05:53 AM, Peter Zijlstra wrote: >>>> On Mon, Feb 13, 2017 at 11:47:16AM +0100, Peter Zijlstra wrote: >>>>> That way we'd end up with something like: >>>>> >>>>> asm(" >>>>> push %rdi; >>>>> movslq %edi, %rdi; >>>>> movq __per_cpu_offset(,%rdi,8), %rax; >>>>> cmpb $0, %[offset](%rax); >>>>> setne %al; >>>>> pop %rdi; >>>>> " : : [offset] "i" (((unsigned long)&steal_time) + offsetof(struct steal_time, preempted))); >>>>> >>>>> And if we could get rid of the sign extend on edi we could avoid all the >>>>> push-pop nonsense, but I'm not sure I see how to do that (then again, >>>>> this asm foo isn't my strongest point). >>>> Maybe: >>>> >>>> movsql %edi, %rax; >>>> movq __per_cpu_offset(,%rax,8), %rax; >>>> cmpb $0, %[offset](%rax); >>>> setne %al; >>>> >>>> ? >>> Yes, that looks good to me. >>> >>> Cheers, >>> Longman >>> >> Sorry, I am going to take it back. The displacement or offset can only >> be up to 32-bit. So we will still need to use at least one more >> register, I think. > I don't think that would be a problem, I very much doubt we declare more > than 4G worth of per-cpu variables in the kernel. > > In any case, use "e" or "Z" as constraint (I never quite know when to > use which). That are s32 and u32 displacement immediates resp. and > should fail compile with a semi-sensible failure if the displacement is > too big. > It is the address of &steal_time that will exceed the 32-bit limit. Cheers, Longman