From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751986AbeBHEKh (ORCPT ); Wed, 7 Feb 2018 23:10:37 -0500 Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:44012 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751269AbeBHEKf (ORCPT ); Wed, 7 Feb 2018 23:10:35 -0500 Date: Wed, 7 Feb 2018 20:10:39 -0800 From: "Paul E. McKenney" To: Steven Rostedt Cc: Matthew Wilcox , Jesper Dangaard Brouer , Kirill Tkhai , josh@joshtriplett.org, mathieu.desnoyers@efficios.com, jiangshanlai@gmail.com, mingo@redhat.com, cl@linux.com, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, rao.shoaib@oracle.com Subject: Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() Reply-To: paulmck@linux.vnet.ibm.com References: <151791170164.5994.8253310844733420079.stgit@localhost.localdomain> <20180207021703.GC3617@linux.vnet.ibm.com> <20180207042334.GA16175@bombadil.infradead.org> <20180207050200.GH3617@linux.vnet.ibm.com> <20180207083104.GK3617@linux.vnet.ibm.com> <20180207085700.393f90d0@gandalf.local.home> <20180207174513.5cc9b503@redhat.com> <20180207181055.GB12446@bombadil.infradead.org> <20180207132619.6595e4a9@gandalf.local.home> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180207132619.6595e4a9@gandalf.local.home> User-Agent: Mutt/1.5.21 (2010-09-15) X-TM-AS-GCONF: 00 x-cbid: 18020804-0056-0000-0000-000004178461 X-IBM-SpamModules-Scores: X-IBM-SpamModules-Versions: BY=3.00008494; HX=3.00000241; KW=3.00000007; PH=3.00000004; SC=3.00000249; SDB=6.00986544; UDB=6.00500676; IPR=6.00765908; BA=6.00005819; NDR=6.00000001; ZLA=6.00000005; ZF=6.00000009; ZB=6.00000000; ZP=6.00000000; ZH=6.00000000; ZU=6.00000002; MB=3.00019434; XFM=3.00000015; UTC=2018-02-08 04:10:31 X-IBM-AV-DETECTION: SAVI=unused REMOTE=unused XFE=unused x-cbparentid: 18020804-0057-0000-0000-0000084EF47D Message-Id: <20180208041039.GR3617@linux.vnet.ibm.com> X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2018-02-08_01:,, signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 priorityscore=1501 malwarescore=0 suspectscore=2 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 impostorscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1709140000 definitions=main-1802080036 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Feb 07, 2018 at 01:26:19PM -0500, Steven Rostedt wrote: > On Wed, 7 Feb 2018 10:10:55 -0800 > Matthew Wilcox wrote: > > > > For the record, I fully agree with Steve here. > > Thanks, but... > > > > > > > And being a performance "fanatic" I don't like to have the extra branch > > > (and compares) in the free code path... but it's a MM-decision (and > > > sometimes you should not listen to "fanatics" ;-)) > > > > While free_rcu() is not withut its performance requirements, I think it's > > currently dominated by cache misses and not by branches. By the time RCU > > gets to run callbacks, memory is certainly L1/L2 cache-cold and probably > > L3 cache-cold. Also calling the callback functions is utterly impossible > > for the branch predictor. > > I agree with Matthew. > > This is far from any fast path. A few extra branches isn't going to > hurt anything here as it's mostly just garbage collection. With or > without the Spectre fixes. What Steve said! Thanx, Paul