From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753724AbcBAVgZ (ORCPT ); Mon, 1 Feb 2016 16:36:25 -0500 Received: from mga11.intel.com ([192.55.52.93]:31866 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751722AbcBAVgY (ORCPT ); Mon, 1 Feb 2016 16:36:24 -0500 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.22,381,1449561600"; d="scan'208";a="40477051" Date: Mon, 1 Feb 2016 13:36:22 -0800 From: Andi Kleen To: Rasmus Villemoes Cc: Andi Kleen , akpm@linux-foundation.org, linux-kernel@vger.kernel.org, davidlohr.bueso@hp.com, rafael.j.wysocki@intel.com, lenb@kernel.org Subject: Re: [PATCH] Optimize int_sqrt for small values for faster idle Message-ID: <20160201213622.GA15302@tassilo.jf.intel.com> References: <1454017365-8509-1-git-send-email-andi@firstfloor.org> <87y4b4azsy.fsf@rasmusvillemoes.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87y4b4azsy.fsf@rasmusvillemoes.dk> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Feb 01, 2016 at 10:25:17PM +0100, Rasmus Villemoes wrote: > On Thu, Jan 28 2016, Andi Kleen wrote: > > > From: Andi Kleen > > > > The menu cpuidle governor does at least two int_sqrt() each time > > we go into idle in get_typical_interval to compute stddev > > > > int_sqrts take 100-120 cycles each. Short idle latency is important > > for many workloads. > > > > If you want to optimize get_typical_interval(), why not just take the > square root out of the equation (literally)? > > Something like Looks good. Yes that's a better fix. -Andi