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 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: linux-arch.vger.kernel.org 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 From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:54424 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1755913AbcJUPJC (ORCPT ); Fri, 21 Oct 2016 11:09:02 -0400 Received: from pps.filterd (m0098416.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.17/8.16.0.17) with SMTP id u9LF4Ysw124105 for ; Fri, 21 Oct 2016 11:09:01 -0400 Received: from e06smtp10.uk.ibm.com (e06smtp10.uk.ibm.com [195.75.94.106]) by mx0b-001b2d01.pphosted.com with ESMTP id 2675yjprtu-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Fri, 21 Oct 2016 11:09:01 -0400 Received: from localhost by e06smtp10.uk.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Fri, 21 Oct 2016 16:08:59 +0100 Subject: Re: [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency References: <1477051138-1610-1-git-send-email-borntraeger@de.ibm.com> <20161021.105727.140184460493941551.davem@davemloft.net> From: Christian Borntraeger Date: Fri, 21 Oct 2016 17:08:54 +0200 MIME-Version: 1.0 In-Reply-To: <20161021.105727.140184460493941551.davem@davemloft.net> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 8bit Message-ID: <2cf23cb7-05c5-0a2d-2ed5-aa90d582f802@de.ibm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: David Miller Cc: peterz@infradead.org, npiggin@gmail.com, linux-kernel@vger.kernel.org, linux-s390@vger.kernel.org, linux-arch@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, heiko.carstens@de.ibm.com, schwidefsky@de.ibm.com, noamc@ezchip.com, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, KVM list Message-ID: <20161021150854.fbPyINSv9RGiXIbeN7yRJ7MyqnEwgRrfQHJj0OTqMW4@z> 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