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 X-Spam-Level: X-Spam-Status: No, score=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 21D20C433E6 for ; Fri, 12 Mar 2021 18:22:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id ED6E364F58 for ; Fri, 12 Mar 2021 18:22:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233072AbhCLSWN (ORCPT ); Fri, 12 Mar 2021 13:22:13 -0500 Received: from mail.kernel.org ([198.145.29.99]:39308 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233086AbhCLSWI (ORCPT ); Fri, 12 Mar 2021 13:22:08 -0500 Received: by mail.kernel.org (Postfix) with ESMTPSA id BE96964F58; Fri, 12 Mar 2021 18:22:07 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linux-foundation.org; s=korg; t=1615573328; bh=J7Tr+mjH9dNiT5fOJvztiH8PtErXkUpo7ilRugFk/Fg=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=yKSWpQNcy99iWhqp91BhfkK0OInKLDXDyCO65EJvoITm0e6a0m+e+HdscraFD8nsI NBPlUJACOxqW+c/3NiGsW9/Z60No4cB9yXJB0sN+VkVh0kMU+v7gLqJcOAkzHOdNSk d6NeqHQIHHUoNtRwNUL/0JQNZwnXfsDbMYAtQAnc= Date: Fri, 12 Mar 2021 10:22:07 -0800 From: Andrew Morton To: Jim Newsome Cc: Oleg Nesterov , "Eric W . Biederman" , Christian Brauner , linux-kernel@vger.kernel.org Subject: Re: [PATCH v5] do_wait: make PIDTYPE_PID case O(1) instead of O(n) Message-Id: <20210312102207.a347e38db375226a78cc37bf@linux-foundation.org> In-Reply-To: <20210312173855.24843-1-jnewsome@torproject.org> References: <20210312173855.24843-1-jnewsome@torproject.org> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 12 Mar 2021 11:38:55 -0600 Jim Newsome wrote: > do_wait is an internal function used to implement waitpid, waitid, > wait4, etc. To handle the general case, it does an O(n) linear scan of > the thread group's children and tracees. > > This patch adds a special-case when waiting on a pid to skip these scans > and instead do an O(1) lookup. This improves performance when waiting on > a pid from a thread group with many children and/or tracees. Could we please see some performance testing results to permit us to evaluate the value of this change? Thanks.