Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932873AbcCRNOE (ORCPT ); Fri, 18 Mar 2016 09:14:04 -0400 Received: from mail-lb0-f193.google.com ([209.85.217.193]:35317 "EHLO mail-lb0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752328AbcCRNOB (ORCPT ); Fri, 18 Mar 2016 09:14:01 -0400 MIME-Version: 1.0 In-Reply-To: <1458274308.6622.79.camel@neuling.org> References: <1454442102-1229-1-git-send-email-shilpa.bhat@linux.vnet.ibm.com> <1454442102-1229-4-git-send-email-shilpa.bhat@linux.vnet.ibm.com> <1458273857.6622.75.camel@neuling.org> <1458274308.6622.79.camel@neuling.org> Date: Fri, 18 Mar 2016 14:13:59 +0100 X-Google-Sender-Auth: 9y5YHxj7fVwbltUkX68gdaENbm8 Message-ID: Subject: Re: [PATCH v8 3/6] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path From: "Rafael J. Wysocki" To: Michael Neuling Cc: Shilpasri G Bhat , linuxppc-dev@ozlabs.org, Linux Kernel Mailing List , "Gautham R. Shenoy" , "linux-pm@vger.kernel.org" , Viresh Kumar , "Rafael J. Wysocki" , pc@us.ibm.com, shreyas@linux.vnet.ibm.com, Anton Blanchard Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1571 Lines: 49 On Fri, Mar 18, 2016 at 5:11 AM, Michael Neuling wrote: > On Fri, 2016-03-18 at 15:04 +1100, Michael Neuling wrote: > >> On Wed, 2016-02-03 at 01:11 +0530, Shilpasri G Bhat wrote: >> > >> > cpu_to_chip_id() does a DT walk through to find out the chip id by >> > taking a contended device tree lock. This adds an unnecessary >> > overhead >> > in a hot path. So instead of calling cpu_to_chip_id() everytime >> > cache >> > the chip ids for all cores in the array 'core_to_chip_map' and use >> > it >> > in the hotpath. >> > >> > Reported-by: Anton Blanchard >> > Signed-off-by: Shilpasri G Bhat >> > Reviewed-by: Gautham R. Shenoy >> > Acked-by: Viresh Kumar >> > --- >> > No changes from v7. >> >> How about this instead? It removes the linear lookup and seems a lot >> less complex. This has gone in already. Can you please send a patch on top of it? > BTW we never init nr_chips before using it. We also need something > like. > > diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c > index d63d2cb..c819ed4 100644 > --- a/drivers/cpufreq/powernv-cpufreq.c > +++ b/drivers/cpufreq/powernv-cpufreq.c > @@ -556,6 +556,8 @@ static int init_chip_info(void) > unsigned int cpu, i; > unsigned int prev_chip_id = UINT_MAX; > > + nr_chips = 0; > + > for_each_possible_cpu(cpu) { > unsigned int id = cpu_to_chip_id(cpu); > > Including this part too maybe? Thanks, Rafael