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 669EEC433F5 for ; Mon, 17 Jan 2022 13:05:12 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id F26586B0071; Mon, 17 Jan 2022 08:05:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id ED5BE6B0073; Mon, 17 Jan 2022 08:05:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id DC6386B0074; Mon, 17 Jan 2022 08:05:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0243.hostedemail.com [216.40.44.243]) by kanga.kvack.org (Postfix) with ESMTP id CE99D6B0071 for ; Mon, 17 Jan 2022 08:05:11 -0500 (EST) Received: from smtpin07.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id 7F3CA824C429 for ; Mon, 17 Jan 2022 13:05:11 +0000 (UTC) X-FDA: 79039799622.07.81C88E3 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf13.hostedemail.com (Postfix) with ESMTP id 8DF8E20009 for ; Mon, 17 Jan 2022 13:05:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=okXnBIihNJ45zjlOgVaV9HIZ4gTPr/ksjRMtNE9fq8A=; b=loMPvfhzX0Y2aCcY8FmyxPWYmv ra70tAkSHGlVnnENkpYDo41jNZOdowzu1iBT8Ud+sM4P5s0MCs7LriwvrzyUaugGV1d3iBS4T4/wr 1eCZPth/HiaKLbdOqeG7fJFvQD9ek/SCCjyW+ZwRhuJs02N3UI80H1KmocLVE5LK7xNc+LWy7Fb3Z B+mQPZpOK9l/3Sa9DoO6FvxXeJI2rSQEYceR1FHe+Y6tR4tEDP9XjYpQUhiAuIjVho7iaEw4kU0Lm 4+Ob2BRbptQZNdbtIQlUZMnCqrYn7D8n9ZRCc7ZxtRn0YN623Al6xsfFPaM3iPX2TkJZrfRHpAyvZ Njv6XwBg==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1n9Rgu-008DFh-Cp; Mon, 17 Jan 2022 13:04:56 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 70B7C300237; Mon, 17 Jan 2022 14:04:54 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 27F832D675215; Mon, 17 Jan 2022 14:04:54 +0100 (CET) Date: Mon, 17 Jan 2022 14:04:54 +0100 From: Peter Zijlstra To: Peter Oskolkov Cc: mingo@redhat.com, tglx@linutronix.de, juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, bristot@redhat.com, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-api@vger.kernel.org, x86@kernel.org, pjt@google.com, posk@google.com, avagin@google.com, jannh@google.com, tdelisle@uwaterloo.ca Subject: Re: [RFC][PATCH 3/3] sched: User Mode Concurency Groups Message-ID: References: <20211214204445.665580974@infradead.org> <20211214205358.701701555@infradead.org> <20211221171900.GA580323@dev-hv> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20211221171900.GA580323@dev-hv> Authentication-Results: imf13.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=loMPvfhz; dmarc=none; spf=none (imf13.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org X-Stat-Signature: rw5fuqtdamjf68tpd3xp3x5ogcjgjhno X-Rspamd-Queue-Id: 8DF8E20009 X-Rspamd-Server: rspam12 X-HE-Tag: 1642424710-460083 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Dec 21, 2021 at 05:19:00PM +0000, Peter Oskolkov wrote: > On Tue, Dec 14, 2021 at 09:44:48PM +0100, Peter Zijlstra wrote: > > +static struct task_struct *umcg_get_task(u32 tid) > > +{ > > + struct task_struct *tsk = NULL; > > + > > + if (tid) { > > + rcu_read_lock(); > > + tsk = find_task_by_vpid(tid); > > + if (tsk && current->mm == tsk->mm && tsk->umcg_task) > > This essentially limits all operations to a single mm/process. > Fine for now, but a fast remote context switch is also a valid use > case. It is not directly related to userspace scheduling, so I'm > just mentioning it here. Maybe server-to-server cross-process > context switches should be allowed for the same user/cgroup? (Again, > this is for later to consider). Doing cross-address-space UMCG will be a massive effort, too much (pretty much everything) in this implementation assumes things are directly addressable. > > + get_task_struct(tsk); > > + else > > + tsk = NULL; > > + rcu_read_unlock(); > > + } > > + > > + return tsk; > > +}