From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Borntraeger Subject: Re: [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency Date: Fri, 21 Oct 2016 17:08:54 +0200 Message-ID: <2cf23cb7-05c5-0a2d-2ed5-aa90d582f802@de.ibm.com> References: <1477051138-1610-1-git-send-email-borntraeger@de.ibm.com> <20161021.105727.140184460493941551.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20161021.105727.140184460493941551.davem@davemloft.net> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: virtualization-bounces@lists.linux-foundation.org Errors-To: virtualization-bounces@lists.linux-foundation.org List-Archive: List-Post: To: David Miller Cc: linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, KVM list , peterz@infradead.org, heiko.carstens@de.ibm.com, linux-kernel@vger.kernel.org, npiggin@gmail.com, virtualization@lists.linux-foundation.org, noamc@ezchip.com, schwidefsky@de.ibm.com, xen-devel@lists.xenproject.org, linuxppc-dev@lists.ozlabs.org List-ID: On 10/21/2016 04:57 PM, David Miller wrote: > From: Christian Borntraeger > Date: Fri, 21 Oct 2016 13:58:53 +0200 > >> For spinning loops people did 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 s390 >> cpu_relax gives up the time slice to the hypervisor. On power cpu_relax >> tries to give some of the CPU to the neighbor threads. To reduce the >> latency another variant cpu_relax_lowlatency was introduced. Before this >> is used in more and more places, lets revert the logic of provide a new >> function cpu_relax_yield that can spend some time and for s390 yields >> the guest CPU. > > Sparc64, fwiw, behaves similarly to powerpc. As sparc currently defines cpu_relax_lowlatency to cpu_relax, this patch set should be a no-op then for sparc, correct? My intend was that cpu_relax should not add a huge latency but can certainly push some cpu power to hardware threads of the same core. This seems to be the case for sparc/power and some arc variants. Christian