From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S941603AbcKOKP1 (ORCPT ); Tue, 15 Nov 2016 05:15:27 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:58965 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S941383AbcKOKPY (ORCPT ); Tue, 15 Nov 2016 05:15:24 -0500 Subject: Re: [GIT PULL v2 0/5] cpu_relax: drop lowlatency, introduce yield To: Peter Zijlstra References: <1477386195-32736-1-git-send-email-borntraeger@de.ibm.com> Cc: 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 , Russell King , virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org From: Christian Borntraeger Date: Tue, 15 Nov 2016 11:15:13 +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: <1477386195-32736-1-git-send-email-borntraeger@de.ibm.com> Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 16111510-0024-0000-0000-0000024C70C4 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 16111510-0025-0000-0000-000021325811 Message-Id: <75f6869e-a2a2-6394-aeda-a30d59b3baa1@de.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-11-15_04:,, 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-1611150189 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 10/25/2016 11:03 AM, Christian Borntraeger wrote: > Peter, > > here is v2 with some improved patch descriptions and some fixes. The > previous version has survived one day of linux-next and I only changed > small parts. > So unless there is some other issue, feel free to pull (or to apply > the patches) to tip/locking. > > The following changes since commit 07d9a380680d1c0eb51ef87ff2eab5c994949e69: > > Linux 4.9-rc2 (2016-10-23 17:10:14 -0700) > > are available in the git repository at: > > git://git.kernel.org/pub/scm/linux/kernel/git/borntraeger/linux.git tags/cpurelax > > for you to fetch changes up to dcc37f9044436438360402714b7544a8e8779b07: > > processor.h: remove cpu_relax_lowlatency (2016-10-25 09:49:57 +0200) Ping. Peter, you had these patches in your https://git.kernel.org/cgit/linux/kernel/git/peterz/queue.git/ repository, but now the patches are gone. Any feedback? > > ---------------------------------------------------------------- > cpu_relax: drop lowlatency, introduce yield > > 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. > > So my proposal boils down to: > - lowest latency: use barrier() or mb() if necessary > - low latency: use cpu_relax (e.g. might give up some cpu for the other > _hardware_ threads) > - really give up CPU: use cpu_relax_yield > > PS: In the long run I would also try to provide for s390 something > like cpu_relax_yield_to with a cpu number (or just add that to > cpu_relax_yield), since a yield_to is always better than a yield as > long as we know the waiter. > > ---------------------------------------------------------------- > Christian Borntraeger (5): > processor.h: introduce cpu_relax_yield > stop_machine: yield CPU during stop machine > s390: make cpu_relax a barrier again > processor.h: Remove cpu_relax_lowlatency users > processor.h: remove cpu_relax_lowlatency > > arch/alpha/include/asm/processor.h | 2 +- > arch/arc/include/asm/processor.h | 4 ++-- > arch/arm/include/asm/processor.h | 2 +- > arch/arm64/include/asm/processor.h | 2 +- > arch/avr32/include/asm/processor.h | 2 +- > arch/blackfin/include/asm/processor.h | 2 +- > arch/c6x/include/asm/processor.h | 2 +- > arch/cris/include/asm/processor.h | 2 +- > arch/frv/include/asm/processor.h | 2 +- > arch/h8300/include/asm/processor.h | 2 +- > arch/hexagon/include/asm/processor.h | 2 +- > arch/ia64/include/asm/processor.h | 2 +- > arch/m32r/include/asm/processor.h | 2 +- > arch/m68k/include/asm/processor.h | 2 +- > arch/metag/include/asm/processor.h | 2 +- > arch/microblaze/include/asm/processor.h | 2 +- > arch/mips/include/asm/processor.h | 2 +- > arch/mn10300/include/asm/processor.h | 2 +- > arch/nios2/include/asm/processor.h | 2 +- > arch/openrisc/include/asm/processor.h | 2 +- > arch/parisc/include/asm/processor.h | 2 +- > arch/powerpc/include/asm/processor.h | 2 +- > arch/s390/include/asm/processor.h | 4 ++-- > arch/s390/kernel/processor.c | 4 ++-- > arch/score/include/asm/processor.h | 2 +- > arch/sh/include/asm/processor.h | 2 +- > arch/sparc/include/asm/processor_32.h | 2 +- > arch/sparc/include/asm/processor_64.h | 2 +- > arch/tile/include/asm/processor.h | 2 +- > arch/unicore32/include/asm/processor.h | 2 +- > arch/x86/include/asm/processor.h | 2 +- > arch/x86/um/asm/processor.h | 2 +- > arch/xtensa/include/asm/processor.h | 2 +- > drivers/gpu/drm/i915/i915_gem_request.c | 2 +- > drivers/vhost/net.c | 4 ++-- > kernel/locking/mcs_spinlock.h | 4 ++-- > kernel/locking/mutex.c | 4 ++-- > kernel/locking/osq_lock.c | 6 +++--- > kernel/locking/qrwlock.c | 6 +++--- > kernel/locking/rwsem-xadd.c | 4 ++-- > kernel/stop_machine.c | 2 +- > lib/lockref.c | 2 +- > 42 files changed, 53 insertions(+), 53 deletions(-) >