From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mout-p-103.mailbox.org (mout-p-103.mailbox.org [80.241.56.161]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id F1E97448D18 for ; Mon, 12 Oct 2026 12:51:40 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=80.241.56.161 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791809503; cv=none; b=Tqo/CN+DIxuYrSxvVTWn+foPEQbHEje45IYBAYku3Um1p0jxsDWNzD+MbeUm57SdPP1ACwwQ/BW8DuLm60z3pKOheiNotSzHknJUhKgLbwg6ZC8N8+9xzKQGSQ0bul5jzaoTecfOlfOkbfStC3FxcGUuJjvrzRTO3/klZKZp4t4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791809503; c=relaxed/simple; bh=itWi7ZYvgSwVgvgCK0mLq3B5wSyyWMCBOvYfkACuTE4=; h=Date:From:To:Cc:Message-ID:In-Reply-To:References:Subject: MIME-Version:Content-Type; b=hAmJiyvVNikui0wdw6fSb37LJMmqNyONzw3YSDCDWivNggdm/BqQZZ3ZYNriRGlrDqDBY74lIDW5BXLyR2RqQicgze8VwqJ3Ot6SoXO7z+WYfpkgiOGZ0TLXf548BUG+Q1mEvHS/fSZ6vzUxsand4NQjfHouPL2BJPXfZYdqk+A= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org; spf=pass smtp.mailfrom=mailbox.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b=gbDLho1O; arc=none smtp.client-ip=80.241.56.161 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=mailbox.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=mailbox.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=mailbox.org header.i=@mailbox.org header.b="gbDLho1O" Received: from smtp2.mailbox.org (smtp2.mailbox.org [IPv6:2001:67c:2050:b231:465::2]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519MLKEM768 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mout-p-103.mailbox.org (Postfix) with ESMTPS id 4j3HQx1g7gzKmBG; Mon, 12 Oct 2026 14:51:37 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mailbox.org; s=mail20150812; t=1791809497; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=ryQaTo3gnu7+iU8fZIemzfLMbvnoZhxtVlWdey7NN18=; b=gbDLho1OnO3bQS7Zqfj3UggPToqMhyQD1ejCXE87bKzRfm/iM0R82CwwnxvXnLbYA5aj/G 19i9R2EP57u0sUTqtn/wN/Gx+o+YMiTrJZp8TpUf6GKH1Nxn//CXRj+L/QvvVFx+WJpUug deOUShGn6KXRCCyMmdtG/UMGcvmqmc1pNxClU7IUgUMSirmMk+rTrNOf5jutA+FIdaVMo7 FIN7QLGc/p0lNDUP1EVjPTIcyExuIWGN1cRWWg5k2p5c5vVOslfgkYQZp/q8kcVepc2ZGy Legr2hKPv2TcQ7N0L0bvyZPyRwTl75XieL0Nl+J/uHc+dEueeWiufXw+WtiVGA== Date: Mon, 12 Oct 2026 14:51:34 +0200 (CEST) From: torvic9@mailbox.org To: Vincent Guittot Cc: peterz@infradead.org, mingo@redhat.com, juri.lelli@redhat.com, dietmar.eggemann@arm.com, kprateek.nayak@amd.com, linux-kernel@vger.kernel.org Message-ID: <57528692.1442403.1791809495018@app.mailbox.org> In-Reply-To: References: <20261002124538.79658-1-torvic9@mailbox.org> Subject: Re: [RFC PATCH 0/2] sched/fair: Remove tunable scaling Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Priority: 3 Importance: Normal X-Mailer: Open-Xchange Mailer v8.52.252 X-Originating-Client: open-xchange-appsuite X-MBO-RS-META: wpc3ziwui9xqxf6ibxoa18nxrt61kjnw X-MBO-RS-ID: cb8a3794fe3ca35bef6 > Vincent Guittot hat am 12.10.2026 14:37 MESZ geschrieben: > > > On Fri, 2 Oct 2026 at 14:45, Tor Vic wrote: > > > > This series removes the scaling of tunables, which was introduced around > > Linux 2.6.33. > > > > I split this into two separate patches: > > > > The first removes the "none" and "linear" scaling which are likely not used much > > and have limited usefulness, as one can always set sched_base_slice through > > debugfs. > > How did you reach this conclusion? and why it's worth removing it > I thought that companies would choose a specific base_slice through sysctl, based upon their needs, but then, I'm not active in the IT segment so I might be wrong. It's possible that there are distributions that use "none" or "linear" by default, but I'm not aware of any. > > It keeps the logarithmic scaling which is already the default. > > > > The second removes the entire scaling mecanism and sets a fixed sched_base_slice > > of 2 milliseconds, a value which has been chosen somewhat arbitrarily. > > No, the sysctl_sched_base_slice value has not been chosen arbitrarily > and the commit you mentioned below gives you the reason That's a misunderstanding. I wanted to say that *I* chose the arbitrary 2 ms in this patchset, not that the kernel's default of 0.7 ms was chosen arbitrarily. > > > > > Currently, the base_slice multiplied by the log2 factor can take the values of > > 0.7 (1 CPU), 1.4 (2-3 CPUs), 2.1 (4-7 CPUs) and 2.8 msecs (8+ CPUs), so it seems > > that the new value of 2 msecs is a sane default, which I also use on my consumer > > x86_64 machines. > > However I'll leave that open for discussion. Note that the base_slice value has > > changed quite often over the years, lastly in 2025 [1]. > > > > The series applies to 7.3-rc5, and is build- and boot tested on a measly 2C/4T > > Skylake machine. I marked it as RFC because I don't know whether these changes > > are actually wanted by the sched people - and because I'm not a developer. > > It does however remove quite a lot of code. > > > > [1] commit 2ae891b826958b60919ea21c727f77bcd6ffcc2c > > > > Tor Vic (2): > > sched/fair: Remove the 'none' and 'linear' scaling of tunables > > sched/fair: Remove sched_base_slice scaling altogether > > > > include/linux/sched/sysctl.h | 7 ---- > > kernel/sched/core.c | 1 - > > kernel/sched/debug.c | 52 ------------------------ > > kernel/sched/fair.c | 79 ++---------------------------------- > > kernel/sched/sched.h | 5 --- > > 5 files changed, 3 insertions(+), 141 deletions(-) > > > > -- > > 2.55.0 > >