From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from shards.monkeyblade.net (shards.monkeyblade.net [184.105.139.130]) by lists.ozlabs.org (Postfix) with ESMTP id 3t0pgZ5rZCzDt14 for ; Sat, 22 Oct 2016 01:57:30 +1100 (AEDT) Date: Fri, 21 Oct 2016 10:57:27 -0400 (EDT) Message-Id: <20161021.105727.140184460493941551.davem@davemloft.net> To: borntraeger@de.ibm.com 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 Subject: Re: [PATCH/RFC 0/5] cpu_relax: introduce yield, remove lowlatency From: David Miller In-Reply-To: <1477051138-1610-1-git-send-email-borntraeger@de.ibm.com> References: <1477051138-1610-1-git-send-email-borntraeger@de.ibm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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.