From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938587AbcKONUd (ORCPT ); Tue, 15 Nov 2016 08:20:33 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:34447 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938148AbcKONU1 (ORCPT ); Tue, 15 Nov 2016 08:20:27 -0500 Subject: Re: [GIT PULL v2 1/5] processor.h: introduce cpu_relax_yield To: Russell King - ARM Linux References: <1477386195-32736-1-git-send-email-borntraeger@de.ibm.com> <1477386195-32736-2-git-send-email-borntraeger@de.ibm.com> <20161115123029.GT1041@n2100.armlinux.org.uk> Cc: Peter Zijlstra , Ingo Molnar , Nicholas Piggin , linux-kernel@vger.kernel.org, linux-s390 , linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, Heiko Carstens , Martin Schwidefsky , Noam Camus , sparclinux@vger.kernel.org, x86@kernel.org, Will Deacon , Catalin Marinas , virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org From: Christian Borntraeger Date: Tue, 15 Nov 2016 14:19:53 +0100 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: <20161115123029.GT1041@n2100.armlinux.org.uk> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111513-0028-0000-0000-0000024BACE6 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111513-0029-0000-0000-0000213850FB Message-Id: <7f7850e4-c7bb-9cc1-2d65-a1555e97988a@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-15_05:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 suspectscore=0 malwarescore=0 phishscore=0 adultscore=0 bulkscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1609300000 definitions=main-1611150240 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/15/2016 01:30 PM, Russell King - ARM Linux wrote: > On Tue, Oct 25, 2016 at 11:03:11AM +0200, Christian Borntraeger wrote: >> For spinning loops people do often use barrier() or cpu_relax(). >> For most architectures cpu_relax and barrier are the same, but on >> some architectures cpu_relax can add some latency. >> For example on power,sparc64 and arc, cpu_relax can shift the CPU >> towards other hardware threads in an SMT environment. >> On s390 cpu_relax does even more, it uses an hypercall to the >> hypervisor to give up the timeslice. >> In contrast to the SMT yielding this can result in larger latencies. >> In some places this latency is unwanted, so another variant >> "cpu_relax_lowlatency" was introduced. Before this is used in more >> and more places, lets revert the logic and provide a cpu_relax_yield >> that can be called in places where yielding is more important than >> latency. By default this is the same as cpu_relax on all architectures. > > Rather than having to update all these architectures in this way, can't > we put in some linux/*.h header something like: > > #ifndef cpu_relax_yield > #define cpu_relax_yield() cpu_relax() > #endif > > so only those architectures that need to do something need to be > modified? These patches are part of linux-next since a month or so, changing that would invalidate all the next testing. If people want that, I can certainly do that, though.