From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751406AbdBMWPm convert rfc822-to-8bit (ORCPT ); Mon, 13 Feb 2017 17:15:42 -0500 Received: from terminus.zytor.com ([65.50.211.136]:41694 "EHLO mail.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750831AbdBMWPk (ORCPT ); Mon, 13 Feb 2017 17:15:40 -0500 Date: Mon, 13 Feb 2017 14:07:51 -0800 User-Agent: K-9 Mail for Android In-Reply-To: <20170213215220.GN25813@worktop.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Subject: Re: [PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function To: Peter Zijlstra , Waiman Long CC: Jeremy Fitzhardinge , Chris Wright , Alok Kataria , Rusty Russell , Ingo Molnar , Thomas Gleixner , 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: hpa@zytor.com Message-ID: <8BDFD84E-33DB-4017-8229-6E87F4F7A861@zytor.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On February 13, 2017 1:52:20 PM PST, 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. Oh, and unless you are explicitly forcing 32-bit addressing mode, displacements are always "e" (or "m" if you let gcc pick the addressing mode.) -- Sent from my Android device with K-9 Mail. Please excuse my brevity.