From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752413AbdGDPcl (ORCPT ); Tue, 4 Jul 2017 11:32:41 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:49053 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752315AbdGDPck (ORCPT ); Tue, 4 Jul 2017 11:32:40 -0400 Date: Tue, 4 Jul 2017 17:32:37 +0200 (CEST) From: Thomas Gleixner To: Davidlohr Bueso cc: LKML , linux-mm@kvack.org, Andrey Ryabinin , Michal Hocko , Andrew Morton , Vlastimil Babka , Vladimir Davydov , Peter Zijlstra Subject: Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem In-Reply-To: <20170704152206.GB11168@linux-80c1.suse> Message-ID: References: <20170704093232.995040438@linutronix.de> <20170704093421.506836322@linutronix.de> <20170704150106.GA11168@linux-80c1.suse> <20170704152206.GB11168@linux-80c1.suse> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 4 Jul 2017, Davidlohr Bueso wrote: > On Tue, 04 Jul 2017, Davidlohr Bueso wrote: > > > As a side effect you end up optimizing get/put_online_mems() at the cost > > of more overhead for the actual hotplug operation, which is rare and of less > > performance importance. > > So nm this, the reader side actually gets _more_ expensive with pcpu-rwsems > due to at least two full barriers for each get/put operation. Compared to a mutex_lock/unlock() pair on a global mutex .... From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wm0-f70.google.com (mail-wm0-f70.google.com [74.125.82.70]) by kanga.kvack.org (Postfix) with ESMTP id 8E1C66B02C3 for ; Tue, 4 Jul 2017 11:32:42 -0400 (EDT) Received: by mail-wm0-f70.google.com with SMTP id p204so24643853wmg.3 for ; Tue, 04 Jul 2017 08:32:42 -0700 (PDT) Received: from Galois.linutronix.de (Galois.linutronix.de. [2a01:7a0:2:106d:700::1]) by mx.google.com with ESMTPS id w201si9688826wme.103.2017.07.04.08.32.41 for (version=TLS1_2 cipher=AES128-SHA bits=128/128); Tue, 04 Jul 2017 08:32:41 -0700 (PDT) Date: Tue, 4 Jul 2017 17:32:37 +0200 (CEST) From: Thomas Gleixner Subject: Re: [patch V2 2/2] mm/memory-hotplug: Switch locking to a percpu rwsem In-Reply-To: <20170704152206.GB11168@linux-80c1.suse> Message-ID: References: <20170704093232.995040438@linutronix.de> <20170704093421.506836322@linutronix.de> <20170704150106.GA11168@linux-80c1.suse> <20170704152206.GB11168@linux-80c1.suse> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Davidlohr Bueso Cc: LKML , linux-mm@kvack.org, Andrey Ryabinin , Michal Hocko , Andrew Morton , Vlastimil Babka , Vladimir Davydov , Peter Zijlstra On Tue, 4 Jul 2017, Davidlohr Bueso wrote: > On Tue, 04 Jul 2017, Davidlohr Bueso wrote: > > > As a side effect you end up optimizing get/put_online_mems() at the cost > > of more overhead for the actual hotplug operation, which is rare and of less > > performance importance. > > So nm this, the reader side actually gets _more_ expensive with pcpu-rwsems > due to at least two full barriers for each get/put operation. Compared to a mutex_lock/unlock() pair on a global mutex .... -- 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