Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751158AbcCREE2 (ORCPT ); Fri, 18 Mar 2016 00:04:28 -0400 Received: from ozlabs.org ([103.22.144.67]:49535 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750719AbcCREET convert rfc822-to-8bit (ORCPT ); Fri, 18 Mar 2016 00:04:19 -0400 Message-ID: <1458273857.6622.75.camel@neuling.org> Subject: Re: [PATCH v8 3/6] cpufreq: powernv: Remove cpu_to_chip_id() from hot-path From: Michael Neuling To: Shilpasri G Bhat , linuxppc-dev@ozlabs.org, linux-kernel@vger.kernel.org Cc: ego@linux.vnet.ibm.com, linux-pm@vger.kernel.org, viresh.kumar@linaro.org, rjw@rjwysocki.net, pc@us.ibm.com, shreyas@linux.vnet.ibm.com, anton@samba.org Date: Fri, 18 Mar 2016 15:04:17 +1100 In-Reply-To: <1454442102-1229-4-git-send-email-shilpa.bhat@linux.vnet.ibm.com> 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> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT X-Mailer: Evolution 3.16.5-1ubuntu3.1 Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1636 Lines: 51 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. Mikey diff --git a/drivers/cpufreq/powernv-cpufreq.c b/drivers/cpufreq/powernv-cpufreq.c index 547890f..d63d2cb 100644 --- a/drivers/cpufreq/powernv-cpufreq.c +++ b/drivers/cpufreq/powernv-cpufreq.c @@ -52,6 +52,7 @@ static struct chip { } *chips; static int nr_chips; +static DEFINE_PER_CPU(unsigned int, chip_id); /* * Note: The set of pstates consists of contiguous integers, the @@ -317,9 +318,7 @@ static void powernv_cpufreq_throttle_check(void *data) pmsr = get_pmspr(SPRN_PMSR); - for (i = 0; i < nr_chips; i++) - if (chips[i].id == cpu_to_chip_id(cpu)) - break; + i = this_cpu_read(chip_id); /* Check for Pmax Capping */ pmsr_pmax = (s8)PMSR_MAX(pmsr); @@ -560,6 +559,7 @@ static int init_chip_info(void) for_each_possible_cpu(cpu) { unsigned int id = cpu_to_chip_id(cpu); + per_cpu(chip_id, cpu) = nr_chips; if (prev_chip_id != id) { prev_chip_id = id; chip[nr_chips++] = id;