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 B5F45C6FD1D for ; Sun, 2 Apr 2023 02:41:19 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230153AbjDBClS (ORCPT ); Sat, 1 Apr 2023 22:41:18 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53896 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229379AbjDBClQ (ORCPT ); Sat, 1 Apr 2023 22:41:16 -0400 Received: from mout.gmx.net (mout.gmx.net [212.227.17.20]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 808E3195 for ; Sat, 1 Apr 2023 19:41:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.de; s=s31663417; t=1680403224; i=efault@gmx.de; bh=F+Umf3hqPFHg7SHeuykhKhJatkHnksiSqUpbWv1gAxk=; h=X-UI-Sender-Class:Subject:From:To:Cc:Date:In-Reply-To:References; b=BIEYbyOXiIo1kGuEzMcB1jGE+9h+YA6XkixIf4O5ksSMBkFSR2Jf042JD7OPYbzeu a4UN/ZmF9Ver9UEpwI9JnXeXGykzLBvl6wXKL7vtO/kNvgn0m++yr9Hc2BsCJ6wioC AVbciXk2eRMFfeqNaf5OKp5+KmPI+5rHi6OU6dC876jT2bcCYcXLYQyAkp7ao7Buq2 MUlTglQyAjXIQyNCuHO1TI5xEAPYIKidfI5hh6ExttHTMoYW036KAJ6pTFDofidKib w1jm89rrSxTSmdlp+95XPWf1YyNXdi1g2JHuf7yuQlY2FVPdgpyzhDnJS4xbg/i4Yi FVGcM5CRvH+/Q== X-UI-Sender-Class: 724b4f7f-cbec-4199-ad4e-598c01a50d3a Received: from homer.fritz.box ([185.221.148.150]) by mail.gmx.net (mrgmx105 [212.227.17.168]) with ESMTPSA (Nemesis) id 1N3siG-1qQYbg0mbg-00zq9q; Sun, 02 Apr 2023 04:40:24 +0200 Message-ID: Subject: Re: [PATCH 14/17] sched/eevdf: Better handle mixed slice length From: Mike Galbraith To: Hillf Danton , Vincent Guittot Cc: mingo@kernel.org, linux-kernel@vger.kernel.org, Peter Zijlstra , rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, corbet@lwn.net, qyousef@layalina.io, joshdon@google.com, timj@gnu.org, kprateek.nayak@amd.com, yu.c.chen@intel.com, youssefesmat@chromium.org, linux-mm@kvack.org, joel@joelfernandes.org Date: Sun, 02 Apr 2023 04:40:20 +0200 In-Reply-To: <20230401232355.336-1-hdanton@sina.com> References: <20230328092622.062917921@infradead.org> <20230328110354.562078801@infradead.org> <20230401232355.336-1-hdanton@sina.com> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:b8jb18m/xLO6WWf/DBSGrQ206CvHmR3HAKRTfTwT2SXID/J1xTQ wDHtip+cCtSUZe3C2WbPiEWAXZXEmFdcq/4JFvJrhBifqyg6VDxb8Cd+nr8HBUnd+i90yu/ 8tnziH/4E5VpjYLpNfSlhS5pL2waZQAAhoK6fvO9S0DtvUYrCOZMVlnsqPa/LPymYMoYWmR wJy+Q6LVN6zZnf6i4CrBA== UI-OutboundReport: notjunk:1;M01:P0:ek+gC82vFZs=;oIfltOHJL24YinxvqsFelGhEouy uXb0O0+r9lTgMmGMVVPJftypXPZdqMPFORGqTh0Ag4ysLMPXHDxmmOSDPI30GWwIpoJrN1uI7 CRNK1a6+hBo20VlMc6UmSjBRlx98fpGW/flc/vc84luSNb+6wGvgD7x0wDJL14GVxcQ53D1m0 4XAgv0Dm+464Bz0N2dDFe1Kts1jKZDoiU6D33t8uIlhL30J+suCjAmUhUJiFfzfKlh6Hit98m oRHLqhRPwq9ovBxnVsW13iQMvXq7Ea2ZZ/F1VuSR03a5sEYtzuVmnwkUWpsacLnQtR2KURKFF 3ga/hBucgatY6pe4FxWrnt8j0RfaOB6ZT+G2BxB9orErRwteKrolrP9Cn/ERvDRqFSSqDmqNb f1KbDDK9cA+YurEyloGOiz8LzmScc5LW0faqY3CqKhO3OCKqKiYr71MVAFUhCUYyUIO9wcTdm Ar9KZzdSJFp6Y7GZzPCjvfoJZKxaVdkV6IuawwGeZ86XZ7ra+2ZmRUyUMrLNL8r+GIszu9wf/ vM92ZnBHKAEj4kyfCRJyr0T9zICMBmjqVv1Be/edyAtaQ9clU1NkwDzHS5607PLnZezHmAVCh 12y9cgbwlxzrslOA9bR/AO0AiveTIX2tiztF49get5/bOE0Fl+iSO+Hah3xri+puHzG5A2NHU lV7OaU09KrotHWL7/hHsE3Jb2hhUoNMYZ4K4kDBHhsw/X1pa0jPzT82m+6r8+w0uYJW3ezkUB F+XFXfh7yAsRbe4hs2FIr8zSuTxNFg82+TxD2RY73vYYXIG/zqJq1PnJBgwlLAjwxEOmqDmW7 5DtJ8rXkj5d6LoSxhrQpBko1DqzD4q9q2PgqRrDhGUoDhBnXDMUl1URirMBXeByt1gxxLOvwc b2hKFGYP2jnKHxVZcU1O8TOgme9ikJwGJH1TQBhISn9owFYGz3n7nxYUIEE9n8VeRcCTk1A5D BKgbjg== Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 2023-04-02 at 07:23 +0800, Hillf Danton wrote: > On 31 Mar 2023 17:26:51 +0200 Vincent Guittot > > > > I wanted to stress this situation with a simple use case but it seems > > that even without changing the slice, there is a fairness problem: > > > > Task A always run > > Task B loops on : running 1ms then sleeping 1ms > > default nice and latency nice prio bot both > > each task should get around 50% of the time. > > > > The fairness is ok with tip/sched/core > > but with eevdf, Task B only gets around 30% > > Convincing evidence for glitch in wakeup preempt. If you turn on PLACE_BONUS, it'll mimic FAIR_SLEEPERS.. but if you then do some testing, you'll probably turn it right back off. The 50/50 split in current code isn't really any more fair, as soon as you leave the tiny bubble of fairness, it's not the least bit fair. Nor is that tiny bubble all rainbows and unicorns, it brought with it benchmark wins and losses, like everything that changes more than comments, its price being service latency variance. The short term split doesn't really mean all that much, some things will like the current fair-bubble better, some eevdf virtual deadline math and its less spiky service. We'll see. I'm kinda hoping eevdf works out, FAIR_SLEEPERS is quite annoying to squabble with. -Mike