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 BE0B2C0015E for ; Tue, 25 Jul 2023 11:22:49 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 3118F8D0002; Tue, 25 Jul 2023 07:22:49 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 2C1F66B0075; Tue, 25 Jul 2023 07:22:49 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 1B0FD8D0002; Tue, 25 Jul 2023 07:22:49 -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 0CE456B0074 for ; Tue, 25 Jul 2023 07:22:49 -0400 (EDT) Received: from smtpin18.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay01.hostedemail.com (Postfix) with ESMTP id CB9831C9D47 for ; Tue, 25 Jul 2023 11:22:48 +0000 (UTC) X-FDA: 81049896816.18.4BAD3C4 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by imf14.hostedemail.com (Postfix) with ESMTP id A1D6F10001C for ; Tue, 25 Jul 2023 11:22:46 +0000 (UTC) Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Ug3Bp0mo; spf=pass (imf14.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1690284166; 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-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=ppk8ETUNP0NDMqZl58ksSGaggp+lxJxzNg5vybESQaE=; b=Xed8iNfYVMdNhe8oCpy2bPYMKTObtMniXhLQN21uVLs4cH5ERjBMfo1Oaexq4cidge4F5F Bde/qusuRyU+SZiQwOTWVZck6Ttg2TxXGiNDlpIvjjlzNV/5aWk3DnqgoGTiCcVg19RgOI 7uOlG5130e901IWuVhr4bCeOz+hAHt8= ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1690284166; a=rsa-sha256; cv=none; b=SIlSDte1fAQ3Zri1KJ3ZPyyAsiNXG7ekNnsoU39auKvsYtmzy/ChkTTG2uBxygue8wrMby n/g+zeO03KdzvubDRgHZ9Rc44CUB0AlzZNmdjfLoIgQjwbTA/vlQM2YC4vo2NN5vnXm8wk etpTDwDgYcJp1dN/c71N3xTKCy+0q5M= ARC-Authentication-Results: i=1; imf14.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Ug3Bp0mo; spf=pass (imf14.hostedemail.com: domain of frederic@kernel.org designates 139.178.84.217 as permitted sender) smtp.mailfrom=frederic@kernel.org; dmarc=pass (policy=none) header.from=kernel.org Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 96A4F616A1; Tue, 25 Jul 2023 11:22:45 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 605A4C433C9; Tue, 25 Jul 2023 11:22:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1690284164; bh=3PZwNojel/fB0iAxHMvVvEfU8vg+2OWEs6gC1RrNPhs=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Ug3Bp0moAtl2iOU0LqyL6tock6eXDiL1XykMzJHwS26YFDBZTp2nVVg5DegFC95W1 wDJLMEHXkEgb5ZX1TQ495uXTpRNdYAXZ0H74hGRGrgpvceN4JFUqF6/WhthIgQOoXb XvH/x8Td6KU4anPDoEwiqQRHT7TSms9g3xsZZT/xKIcjy12Z7QZkhJPm6IYHGnAxUf /7VrDt7orGvGidvZWlI4CS9xmnPnE8482azX1QUUGJEU3qAo3Aq5g2wHoRF8lZwyFA aKaa6T74oelllGzL5yE1ufrOMNi/c0qdUFY7RpOaL4AoiPSzhULoGduWnosuWAb/0L PhJHNPXC3RiRg== Date: Tue, 25 Jul 2023 13:22:42 +0200 From: Frederic Weisbecker To: Valentin Schneider Cc: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, linux-doc@vger.kernel.org, kvm@vger.kernel.org, linux-mm@kvack.org, bpf@vger.kernel.org, x86@kernel.org, rcu@vger.kernel.org, linux-kselftest@vger.kernel.org, Nicolas Saenz Julienne , Steven Rostedt , Masami Hiramatsu , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Paolo Bonzini , Wanpeng Li , Vitaly Kuznetsov , Andy Lutomirski , Peter Zijlstra , "Paul E. McKenney" , Neeraj Upadhyay , Joel Fernandes , Josh Triplett , Boqun Feng , Mathieu Desnoyers , Lai Jiangshan , Zqiang , Andrew Morton , Uladzislau Rezki , Christoph Hellwig , Lorenzo Stoakes , Josh Poimboeuf , Jason Baron , Kees Cook , Sami Tolvanen , Ard Biesheuvel , Nicholas Piggin , Juerg Haefliger , Nicolas Saenz Julienne , "Kirill A. Shutemov" , Nadav Amit , Dan Carpenter , Chuang Wang , Yang Jihong , Petr Mladek , "Jason A. Donenfeld" , Song Liu , Julian Pidancet , Tom Lendacky , Dionna Glaze , Thomas =?iso-8859-1?Q?Wei=DFschuh?= , Juri Lelli , Daniel Bristot de Oliveira , Marcelo Tosatti , Yair Podemsky Subject: Re: [RFC PATCH v2 15/20] context-tracking: Introduce work deferral infrastructure Message-ID: References: <20230720163056.2564824-1-vschneid@redhat.com> <20230720163056.2564824-16-vschneid@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: g6cyyyc7819gue9h4jxhdztojfknngfd X-Rspamd-Server: rspam10 X-Rspamd-Queue-Id: A1D6F10001C X-Rspam-User: X-HE-Tag: 1690284166-37708 X-HE-Meta: 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 NVjQN18e 3C47/X8ARc9bcaleY7/evt+xN2b7ZcnP4y1Fi6Q5QaodeIt6moe+OeT9FQrScw6oQkGTBmI07CsCfbpy0oLwRfH4RPUGLBqxkLdV+0IjMVDVBtRF+4lAjnMrshIP9AS2xoicJp3RbXNwjE40vfWmqoRIVsosFgAq3xYxhT+eeb/d6+5vTNAvIVHl2MRpvMXb6ppMBSmWuw7SA8CW5dEwlOkQQ1Rwg3fiL+Ia+yGIsq67gyL5bO64BXSlc4efeOSX/RsoZzSjB1oVZF/oEAda/OQ0X8XYkOIuo4ZNyvPTW5UPcbfAhCzrCa1IQ9xVOtQO7VsA32W1QygW9umeE1ZZim90XwtX4WRYbFNILVXO1biBqzXU= 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, Jul 25, 2023 at 11:10:31AM +0100, Valentin Schneider wrote: > I have reasons! I just swept them under the rug and didn't mention them :D > Also looking at the config dependencies again I got it wrong, but > nevertheless that means I get to ramble about it. > > With NO_HZ_IDLE, we get CONTEXT_TRACKING_IDLE, so we get these > transitions: > > ct_idle_enter() > ct_kernel_exit() > ct_state_inc_clear_work() > > ct_idle_exit() > ct_kernel_enter() > ct_work_flush() > > Now, if we just make CONTEXT_TRACKING_WORK depend on CONTEXT_TRACKING_IDLE > rather than CONTEXT_TRACKING_USER, we get to leverage the IPI deferral for > NO_HZ_IDLE kernels - in other words, we get to keep idle CPUs idle longer. > > It's a completely different argument than reducing interference for > NOHZ_FULL userspace applications and I should have at the very least > mentioned it in the cover letter, but it's the exact same backing > mechanism. > > Looking at it again, I'll probably make the CONTEXT_IDLE thing a separate > patch with a proper changelog. Ok should that be a seperate Kconfig? This indeed can bring power improvement but at the cost of more overhead from the sender. A balance to be measured...