From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753179Ab3KSTOy (ORCPT ); Tue, 19 Nov 2013 14:14:54 -0500 Received: from merlin.infradead.org ([205.233.59.134]:46747 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752621Ab3KSTOw (ORCPT ); Tue, 19 Nov 2013 14:14:52 -0500 Date: Tue, 19 Nov 2013 20:14:34 +0100 From: Peter Zijlstra To: Ingo Molnar Cc: Linus Torvalds , Josh Boyer , Linux Kernel Mailing List , Thomas Gleixner , "H. Peter Anvin" , Andrew Morton , Josh Boyer , Rusty Russell Subject: Re: [GIT PULL] core kernel update Message-ID: <20131119191434.GQ16796@laptop.programming.kicks-ass.net> References: <20131119154253.GA12219@gmail.com> <20131119190904.GA22076@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20131119190904.GA22076@gmail.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Nov 19, 2013 at 08:09:04PM +0100, Ingo Molnar wrote: > The actual value of the limit - here's the on-stack cpumask sizes of > the candidate range: > > 128 CPUs: 16 byte cpumasks > 256 CPUs: 32 byte cpumasks > 512 CPUs: 64 byte cpumasks So 512 / 64bytes is a single cacheline and feels like a nice cut-off before requiring an extra indirection and more cachelines. 64 bytes also doesn't sound _that_ big to have on-stack. So I'd go for having the cut-off on >512, unless of course theres evidence 64bytes is already too much.