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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 A2DFEC352A4 for ; Wed, 12 Feb 2020 20:03:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 7416E21739 for ; Wed, 12 Feb 2020 20:03:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1581537827; bh=Zf7NBUAek1yLzN1x6/9lISUJiqE/o1AkQy75wlqY+I0=; h=References:In-Reply-To:From:Date:Subject:To:Cc:List-ID:From; b=Kw1Rj+lKctaCoRLmrrTaFBUgS/7UEG9vMDXVgeuhRjTYqpq1awS4SsC16BL0K+/22 p/J5mLdpuCz5Pp48GDlYTmi6H9Ci8LcZrPJ3iGmT+GhWS/bvC7FjMsCSg4CjT97Zqu bDU724o28LpP3bD0IQJhuWl8MAHRG+iBZSa5hjmQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729101AbgBLUDr (ORCPT ); Wed, 12 Feb 2020 15:03:47 -0500 Received: from mail-lf1-f66.google.com ([209.85.167.66]:39962 "EHLO mail-lf1-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727600AbgBLUDq (ORCPT ); Wed, 12 Feb 2020 15:03:46 -0500 Received: by mail-lf1-f66.google.com with SMTP id c23so2505043lfi.7 for ; Wed, 12 Feb 2020 12:03:45 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linux-foundation.org; s=google; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=BPPHdbNaIkwiUwi0XK7V81BmqTqsxD9Wh/eCAuOFZ7c=; b=edEbWD8VWSEo0ZJ6AJhYjMiocwqPWZuh1eMEPANkqs/U4/0xnwRt7xq+7HnenPiGeJ VFphHJXoMrc/FwJ+qGT7Ukw5K8rPi428h9mf6Q5VDFjXFC52E+csZrxYeIflstJkvyxz 55c6XXfz4qcfrKgrhUQu/+BijxMyjycSx/JE8= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=BPPHdbNaIkwiUwi0XK7V81BmqTqsxD9Wh/eCAuOFZ7c=; b=WYKAS3TMw8ktB7ZldVI9NP3am0LjMD8ROXiax5fLlKflRVP69P51tpe1Nqg6kCcp5x 13GEj8W+F4FLEtIKusOwtmK1qu85jywqAgsdvEqKnds6fCftRz9cA8QxEYqrTF9ySzdi 5deRnSi0O5Yj3gTfRcOO0w/ZAG+/Mr2/zVaseHyMfCi/Kc9lmzeKv+Fi530gtvhg9cMc NK01WcEbkasSGbbp202XpJMZiTGOhLIfOtDaxbKnBMkI45KSmittbZgbZ54CCJx8CT9L kB/o94Wkcs3oqUN8QreOCnYl9+w8p9RKGrKD5jOG2qtt6PohpPnoveVm+OeDJrJcF1Hy 8LHA== X-Gm-Message-State: APjAAAXi7IcgFdb6l3DwQyWEXvI+MiNu74s+h71AnR9KIGdyQiabnRZu Ini2pwTDet2+bC261cieLMy1YU9m7To= X-Google-Smtp-Source: APXvYqx2ADEwD/Xh1Y2Ww/lpQ7t9cQfjl6n3jCgyzd3/ZjXQBsZIcio8b07nTcTjdhCMQOldIcQ9ng== X-Received: by 2002:ac2:52a5:: with SMTP id r5mr7470050lfm.19.1581537824190; Wed, 12 Feb 2020 12:03:44 -0800 (PST) Received: from mail-lj1-f179.google.com (mail-lj1-f179.google.com. [209.85.208.179]) by smtp.gmail.com with ESMTPSA id f16sm104445ljn.17.2020.02.12.12.03.43 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 12 Feb 2020 12:03:43 -0800 (PST) Received: by mail-lj1-f179.google.com with SMTP id y6so3823164lji.0 for ; Wed, 12 Feb 2020 12:03:43 -0800 (PST) X-Received: by 2002:a2e:88c5:: with SMTP id a5mr8860316ljk.201.1581537822998; Wed, 12 Feb 2020 12:03:42 -0800 (PST) MIME-Version: 1.0 References: <20200208083604.GA86051@localhost> In-Reply-To: <20200208083604.GA86051@localhost> From: Linus Torvalds Date: Wed, 12 Feb 2020 12:03:26 -0800 X-Gmail-Original-Message-ID: Message-ID: Subject: Re: Applying pipe fix this merge window? To: Josh Triplett Cc: Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, Feb 8, 2020 at 12:36 AM Josh Triplett wrote: > > I've been hammering on your pipe fix patch (switching to exclusive wait > queues) for a month or so, on several different systems, and I've run > into no issues with it. The patch *substantially* improves parallel > build times on large (~100 CPU) systems, both with parallel make and > with other things that use make's pipe-based jobserver. Hmm. I just applied the doc fix that Randy sent, and that made me revisit this commit and the commit message. And I realized that I find it surprising that it makes your build times noticeably better. Yes, I have that silly example program to show the issue in the commit message, and yes, the exclusive directed write->read wakeups should most definitely improve by that commit. But the make jobserver code ends up using "poll()/pselect()" and non-blocking reads, because of how it handles the child death signals. Which means that none of the nice exclusive directed write->read wakeups should even trigger in the first place, because the readers never block, and he poll/pselect code doesn't use exclusive wakeups (because it can't - it doesn't actually consume the data). So I was looking at it, and going "it should actually not help GNU jobserver at all" in the fixed jobserver case. So humor me, Josh - can you try to figure out why your numbers changed for this commit? Linus