From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 56E3DC433EF for ; Sun, 28 Nov 2021 05:11:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229572AbhK1FPN (ORCPT ); Sun, 28 Nov 2021 00:15:13 -0500 Received: from rere.qmqm.pl ([91.227.64.183]:13421 "EHLO rere.qmqm.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229653AbhK1FNN (ORCPT ); Sun, 28 Nov 2021 00:13:13 -0500 Received: from remote.user (localhost [127.0.0.1]) by rere.qmqm.pl (Postfix) with ESMTPSA id 4J1xPH1FPPz4f; Sun, 28 Nov 2021 06:09:55 +0100 (CET) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=rere.qmqm.pl; s=1; t=1638076195; bh=oUZYFQUmcrcLe+khMfxoyii9jHAFHFy8/qX4bg6ScHU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=JnSDJhb2/wFE1+K5BEKj3l92hAUJYMSiQfvzp+ZlCATcD11ALuloHBV8agVwt/D5m 6xO5KVkS6ds9BhnvUIzgpE+GOAlwIHTeHWZUDQLRlCqXrEtKOnOW/XLCrUHjRtkpA+ s0Zgh/IC7vC3LAsHBRaM+HBKV7zFjzE+7UOTFGbokGiHbpHQX7rXsKsJST3S+JBeda 2sNRV1hDCglR6IzM+jk8O4GqGLON53RjQjMI9dzQcjIf9OmuQDCgevPa74eYKb6N8i DO41zxtTZnaEDqhBVPy9rAwcuQc/n0JQGJK3acFZNX84ZqpVMLYjA4M2TxieYk4Vj5 b6s4KzCtg6yrQ== X-Virus-Status: Clean X-Virus-Scanned: clamav-milter 0.103.3 at mail Date: Sun, 28 Nov 2021 06:09:53 +0100 From: =?iso-8859-2?Q?Micha=B3_Miros=B3aw?= To: Yury Norov Cc: linux-kernel@vger.kernel.org, bcm-kernel-feedback-list@broadcom.com, kvm@vger.kernel.org, linux-alpha@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-crypto@vger.kernel.org, linux-csky@vger.kernel.org, linux-ia64@vger.kernel.org, linux-mips@vger.kernel.org, linux-mm@kvack.org, linux-perf-users@vger.kernel.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org, linux-snps-arc@lists.infradead.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 7/9] lib/cpumask: add num_{possible,present,active}_cpus_{eq,gt,le} Message-ID: References: <20211128035704.270739-1-yury.norov@gmail.com> <20211128035704.270739-8-yury.norov@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-2 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-csky@vger.kernel.org On Sun, Nov 28, 2021 at 05:56:51AM +0100, Michał Mirosław wrote: > On Sat, Nov 27, 2021 at 07:57:02PM -0800, Yury Norov wrote: > > Add num_{possible,present,active}_cpus_{eq,gt,le} and replace num_*_cpus() > > with one of new functions where appropriate. This allows num_*_cpus_*() > > to return earlier depending on the condition. > [...] > > @@ -3193,7 +3193,7 @@ int __init pcpu_page_first_chunk(size_t reserved_size, > > > > /* allocate pages */ > > j = 0; > > - for (unit = 0; unit < num_possible_cpus(); unit++) { > > + for (unit = 0; num_possible_cpus_gt(unit); unit++) { > > This looks dubious. The old version I could hope the compiler would call > num_possible_cpus() only once if it's marked const or pure, but the > alternative is going to count the bits every time making this a guaranteed > O(n^2) even though the bitmap doesn't change. Hmm. This code already unnecessarily calls num_possible_cpus() multiple times. Since it doesn't change after early init I would suggest just calling it once here. Best Regards Michał Mirosław