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 kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3F30C433FE for ; Thu, 13 Oct 2022 01:44:03 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 48F956B0071; Wed, 12 Oct 2022 21:44:03 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 43F996B0073; Wed, 12 Oct 2022 21:44:03 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 306FC6B0074; Wed, 12 Oct 2022 21:44:03 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0012.hostedemail.com [216.40.44.12]) by kanga.kvack.org (Postfix) with ESMTP id 1EECB6B0071 for ; Wed, 12 Oct 2022 21:44:03 -0400 (EDT) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay03.hostedemail.com (Postfix) with ESMTP id E7EA4A015E for ; Thu, 13 Oct 2022 01:44:02 +0000 (UTC) X-FDA: 80014230324.23.34F14C1 Received: from mail3-167.sinamail.sina.com.cn (mail3-167.sinamail.sina.com.cn [202.108.3.167]) by imf09.hostedemail.com (Postfix) with ESMTP id 383BC140022 for ; Thu, 13 Oct 2022 01:44:00 +0000 (UTC) Received: from unknown (HELO localhost.localdomain)([114.249.60.223]) by sina.com (172.16.97.32) with ESMTP id 63476CE9000243DB; Thu, 13 Oct 2022 09:42:03 +0800 (CST) X-Sender: hdanton@sina.com X-Auth-ID: hdanton@sina.com X-SMAIL-MID: 401294630704 From: Hillf Danton To: Qais Yousef Cc: John Stultz , LKML , linux-mm@kvack.org, Connor O'Brien , Peter Zijlstra , Steven Rostedt Subject: Re: [RFC PATCH v4 2/3] sched: Avoid placing RT threads on cores handling long softirqs Date: Thu, 13 Oct 2022 09:43:47 +0800 Message-Id: <20221013014347.104-1-hdanton@sina.com> In-Reply-To: <20221012141037.5cm3mzmnsz5wt36z@wubuntu> References: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit ARC-Authentication-Results: i=1; imf09.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf09.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.167 as permitted sender) smtp.mailfrom=hdanton@sina.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1665625442; a=rsa-sha256; cv=none; b=b6vGy8XugSW/QPdAPwhhfSmBoroSUn8j30QcFDsicgF8Uqf4pFyGhWBSUOVxAwBDUUWeUJ nCYLZKiOYO38WWDLRYm2bEraBeELuUnNUmcdW49KAlfwfguQYghEDyVW0Nkz7Na7uSZjJj 8ifOEZ95ciiF5xErYR5s6Zjq/ELTAbE= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1665625442; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=+Ehls7hC+KWZesbXHjQkcQxXGbn/NUclwAcnpCZ4u4g=; b=ctM76Y2wEPAEb8+X/ox6aXwQMyYvye4rKXmHzNWz9Lhv4uhwI9SROoDJfqNxWKrqwq1zmb PPpyjRbL+kX4If6m+y3tls8y5BA7VFzsHZREW19Iud4zJ8r30pNon8TsD1D86S991OLHrG fIDYb8eqkgVcOyfN12sGKlcx9AWkWkM= X-Rspam-User: Authentication-Results: imf09.hostedemail.com; dkim=none; dmarc=none; spf=pass (imf09.hostedemail.com: domain of hdanton@sina.com designates 202.108.3.167 as permitted sender) smtp.mailfrom=hdanton@sina.com X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 383BC140022 X-Stat-Signature: 9m6jdfbeapofzxxsgi5hep5t98g34b1p X-HE-Tag: 1665625440-592064 X-Bogosity: Ham, tests=bogofilter, spamicity=0.051837, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 12 Oct 2022 15:10:37 +0100 Qais Yousef > On 10/11/22 19:18, Hillf Danton wrote: > > > The issue at hand here is that the softirqs boundedness is hard to control. And > > > the scheduling delays ensued are hard to deal with by any sys-admin. > > > > > Given "The RT scheduler is for tasks that require strick scheduling > > requirements over all else, including performance." [1], I would invite > > Steve to shed some more light on the relation between RT scheduler and > > performance/network throughputs. > > > > Bonus question, why softirq took no care of RT tasks, given strick > > scheduling requirements above? > > > > [1] https://lore.kernel.org/lkml/257E96C2-6ABD-4DD6-9B7F-771DA3D1BAAA@goodmis.org/ > > I think you're mixing the two patches up. Nope, see below. > That patch is to help describe some > latency requirements for CFS tasks. It has nothing to do with RT. Your Correct. > suggestion to use RT scheduler is not valid as these tasks can't be converted > to RT. My suggestion [2,3] to that patch is add a mild change to tick preempt. [2] https://lore.kernel.org/all/20221008103439.107-1-hdanton@sina.com/ [3] https://lore.kernel.org/all/20220920113238.1176-1-hdanton@sina.com/ > Which is what Steve was trying to say IIUC. No followup. > > Generally converting normal application tasks into RT is a recipe for disaster > because: > > 1. Misbehaving RT tasks (busy looping indefinitely) can hog the system > to a halt. > 2. How do you manage priorities of all these pseudo-random RT tasks > each application spawns so you end up with correct resource sharing? Thanks for good material. > > ie: using RT policy is a privileged operation for a reason :-) Take note. Hillf