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 AF97BC4167D for ; Fri, 14 Jan 2022 15:17:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 41B6F6B0072; Fri, 14 Jan 2022 10:17:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 3CC1C6B0074; Fri, 14 Jan 2022 10:17:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 294096B0075; Fri, 14 Jan 2022 10:17:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0233.hostedemail.com [216.40.44.233]) by kanga.kvack.org (Postfix) with ESMTP id 19C346B0072 for ; Fri, 14 Jan 2022 10:17:14 -0500 (EST) Received: from smtpin20.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay03.hostedemail.com (Postfix) with ESMTP id C03B182E819C for ; Fri, 14 Jan 2022 15:17:13 +0000 (UTC) X-FDA: 79029245946.20.025C8ED Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) by imf24.hostedemail.com (Postfix) with ESMTP id 48D56180017 for ; Fri, 14 Jan 2022 15:17:12 +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=HIRvcwlSl4Hp1A2rT9yMEOxIWfhwKnmROPnxOG/25YE=; b=MLdEMXb4SCvNvAol4jQBhoZrDw ls0LbGXaMsBPr5myQwSrS7mm891UDbP7d0aB9f4apmNBECNtiID+VWfx52VHds1RymMbnwNkWl3UZ uXqRMmCE7eCW15t3NcyRYgr40FR9PAbyMpDMKo+4VVqlAo6j3Za51gppGoB6xxlmWLgexYnbKyFOX FQssGbBTPx6anq/Gxt2YEa+gHIqTTeO/DpsQLsAiLPvbwHucX3ZFedtzFE04M0xVHMJJmtGuB3QtZ 0YORWbZUwdCE60GdjX4gvo5ZhMwkhQ84SmqyNXAk5H+iQhQdIYyGA07EH7KLCc24+jKSIgsY3CCIQ wGoiQw4g==; 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 1n8OK0-005tS8-Ou; Fri, 14 Jan 2022 15:16:57 +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) server-digest SHA256) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id D88AD3002C1; Fri, 14 Jan 2022 16:16:53 +0100 (CET) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id B4C2923CDA75B; Fri, 14 Jan 2022 16:16:53 +0100 (CET) Date: Fri, 14 Jan 2022 16:16:53 +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: X-Stat-Signature: gnggr6i5rn1u9x4484jpsf5nmj7ah18x Authentication-Results: imf24.hostedemail.com; dkim=pass header.d=infradead.org header.s=casper.20170209 header.b=MLdEMXb4; dmarc=none; spf=none (imf24.hostedemail.com: domain of peterz@infradead.org has no SPF policy when checking 90.155.50.34) smtp.mailfrom=peterz@infradead.org X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 48D56180017 X-HE-Tag: 1642173432-814854 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 Fri, Jan 14, 2022 at 03:09:55PM +0100, Peter Zijlstra wrote: > > I think the assumption is based on the idea that a process > > using UMCG will get affined to N CPUs, will have N servers and > > a number of workers, and they will all happily cooperate and not > > get any extra threads running. > > > > Of course the pretty picture was not completely true, as the unblocked > > tasks do consume extra threads in the kernel, though never in the > > userspace. > > Right, there is some unmanaged time anyway. Also, since we force wake to the same CPU, and overlapping runtime is 'short', they should all stick to the same CPU, even if we don't pin.