From owner-freebsd-stable@freebsd.org Mon Jan 23 18:09:29 2017 Return-Path: Delivered-To: freebsd-stable@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id DE56ECBE1F5 for ; Mon, 23 Jan 2017 18:09:29 +0000 (UTC) (envelope-from kob6558@gmail.com) Received: from mail-wm0-x22f.google.com (mail-wm0-x22f.google.com [IPv6:2a00:1450:400c:c09::22f]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority G2" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 71F707A8 for ; Mon, 23 Jan 2017 18:09:29 +0000 (UTC) (envelope-from kob6558@gmail.com) Received: by mail-wm0-x22f.google.com with SMTP id c85so145273218wmi.1 for ; Mon, 23 Jan 2017 10:09:29 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=mime-version:sender:in-reply-to:references:from:date:message-id :subject:to:cc; bh=MTu++kI0qaBu/y7kwKFiwk0i3hOtAdNUnYte3OAKY2c=; b=fmn3gtnXl0l6N4IH/Sm/xb14LQyYHM27APnz/xz2TGLkZzN3R7wisyzfcxMKKMIGsA 9kT6ZOiKH4qYODOzh6urFPBOuDrZwzpfG5sw9G0/CGgzb67AdSq3wJ8K1h+J/Wx71ASN JZ9ZNPhZNxAx3NG0vQcy1XCbeUNyKP3Gxx1khRUjSMmfquYtG32lA3feNu93lATubxgF g3Ca/fRE8O734A2PUa5i/XrI0IIagdVPBYL/K3BHvt6LWcabXwL/te4jIZtvuNj0+rbK HU74ZMxrhQD+u2RINzZawYBszeRKfQ9tCo10NQQakFJzLsUad2YMSCts6FwqB3h+fkOW KsCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:sender:in-reply-to:references:from :date:message-id:subject:to:cc; bh=MTu++kI0qaBu/y7kwKFiwk0i3hOtAdNUnYte3OAKY2c=; b=kH96/85idLcwkiOUliMODJ1FpYtpS2tdFOu3PMRt1U+WLQCLkxfGhDrJKSY+6Ht81V BAF8T8lahMruP8+L1wUn9YDDvlmKOaC+i30Va9IThe1FoMferkNah44uq61NXcFb8TX/ F/D/yl623PVVlglTTWxVYRGgV9LTM5hRZLHkKdm+3yaY2GI0irl/B5TLqS5BdB6lZqHd IgHp5Rc5DKDe315tIKpGJJ9jFUwmC3uTh4IcWYiQkfrUZtXu2YRg5ac4g+iwjDqqtiUm hmwNHvA4IkeEHdmy/5/G255BOnWtMjQ3UpUXlpKF9GvbMz2bYispPe7JY3mhq7RaAM3D RDsw== X-Gm-Message-State: AIkVDXL3SS7sRKY74C4uUjNLfzeHQZZJ+91DYElf6ef/bEk9M5JJSPIQ+uxr2Y0TOFYQJhT56Kuy8ApaWEaCBg== X-Received: by 10.28.147.72 with SMTP id v69mr15363496wmd.51.1485194967686; Mon, 23 Jan 2017 10:09:27 -0800 (PST) MIME-Version: 1.0 Sender: kob6558@gmail.com Received: by 10.28.41.194 with HTTP; Mon, 23 Jan 2017 10:09:27 -0800 (PST) In-Reply-To: <44k29l27f2.fsf@lowell-desk.lan> References: <44k29l27f2.fsf@lowell-desk.lan> From: Kevin Oberman Date: Mon, 23 Jan 2017 10:09:27 -0800 X-Google-Sender-Auth: 1-jywwsfBAaLuYXHI56yfmv5y2w Message-ID: Subject: Re: Building Kernel and World with -j To: FreeBSD-STABLE Mailing List Cc: Walter Parker Content-Type: text/plain; charset=UTF-8 X-Content-Filtered-By: Mailman/MimeDel 2.1.23 X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 23 Jan 2017 18:09:30 -0000 On Mon, Jan 23, 2017 at 6:10 AM, Lowell Gilbert < freebsd-stable-local@be-well.ilk.org> wrote: > Walter Parker writes: > > > For decades there has always been a warning not to do parallel builds of > > the kernel or the world (Linux kernel builds also suggest not to do > this). > > > > Every once in a while, I see people post about 5 minutes. This only way I > > can see this happening is by doing a parallel build (-j 16 on a Xeon > > Monster box). > > > > Are parallel builds safe? If not, what are actual risk factors and can > they > > be mitigated? > > As a general rule, it's safe. But don't report failures from a > parallel build. > > This is not so much an issue of parallel builds being unsupported > as of the logs being harder to read. Use of parallel builds of world and kernel are and have been supported since at least 10.0. If a parallel build fails, the first step is usually to do a single-job build. If it succeeds, there is a bug in the make scripts that should be reported. If the single-job build also fails, a bug should be reported with any errors included from the non-parallel build as the parallel build makes the error context very difficult or even impossible to determine from the log. Generally, I think the number of jobs should be slightly greater than the number of available CPU threads. Back in 10.0 days I ran some tests that showed the for 4 and 8 thread systems the improvements for large numbers of jobs peaked at about CPU thread count + 2 and significantly larger numbers of jobs caused a slight deterioration in performance. This was not true on early hyper-threaded CPUs which did not effectively optimize hyper-threading and things may have changed in the 6 or 7 years since I tested and may be very different for systems with large numbers of threads seen in servers today. -- Kevin Oberman, Part time kid herder and retired Network Engineer E-mail: rkoberman@gmail.com PGP Fingerprint: D03FB98AFA78E3B78C1694B318AB39EF1B055683