From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754349AbcKONiZ (ORCPT ); Tue, 15 Nov 2016 08:38:25 -0500 Received: from pandora.armlinux.org.uk ([78.32.30.218]:42608 "EHLO pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752174AbcKONiW (ORCPT ); Tue, 15 Nov 2016 08:38:22 -0500 Date: Tue, 15 Nov 2016 13:37:58 +0000 From: Russell King - ARM Linux To: Christian Borntraeger 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 Subject: Re: [GIT PULL v2 1/5] processor.h: introduce cpu_relax_yield Message-ID: <20161115133758.GV1041@n2100.armlinux.org.uk> 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> <7f7850e4-c7bb-9cc1-2d65-a1555e97988a@de.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <7f7850e4-c7bb-9cc1-2d65-a1555e97988a@de.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 15, 2016 at 02:19:53PM +0100, Christian Borntraeger wrote: > 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. It's three weeks since you posted them. For one of those weeks (the week you posted them) I was away, and missed them while catching up. Sorry, but it sometimes takes a while to spot things amongst the backlog, and normally takes some subsequent activity on the thread to bring it back into view. -- RMK's Patch system: http://www.armlinux.org.uk/developer/patches/ FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up according to speedtest.net.