From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f69.google.com (mail-pg0-f69.google.com [74.125.83.69]) by kanga.kvack.org (Postfix) with ESMTP id BBA7E6B0359 for ; Wed, 7 Feb 2018 13:26:23 -0500 (EST) Received: by mail-pg0-f69.google.com with SMTP id w19so622713pgv.4 for ; Wed, 07 Feb 2018 10:26:23 -0800 (PST) Received: from mail.kernel.org (mail.kernel.org. [198.145.29.99]) by mx.google.com with ESMTPS id u145si1253021pgb.358.2018.02.07.10.26.22 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 07 Feb 2018 10:26:22 -0800 (PST) Date: Wed, 7 Feb 2018 13:26:19 -0500 From: Steven Rostedt Subject: Re: [PATCH 0/2] rcu: Transform kfree_rcu() into kvfree_rcu() Message-ID: <20180207132619.6595e4a9@gandalf.local.home> In-Reply-To: <20180207181055.GB12446@bombadil.infradead.org> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Matthew Wilcox Cc: Jesper Dangaard Brouer , "Paul E. McKenney" , 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 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. -- Steve -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org