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 9E63CC433EF for ; Mon, 30 May 2022 08:12:00 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232080AbiE3IL6 (ORCPT ); Mon, 30 May 2022 04:11:58 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39642 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233169AbiE3IL4 (ORCPT ); Mon, 30 May 2022 04:11:56 -0400 Received: from casper.infradead.org (casper.infradead.org [IPv6:2001:8b0:10b:1236::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id B9D0C2DD2; Mon, 30 May 2022 01:11:52 -0700 (PDT) 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=sasIzphq1eZBnQQmU0BcAocyi+BZTjrLXEHfOoMPumM=; b=b+Ks2J8SjZtMjYzBxr684T+0R7 m9CzQy5jUaP+gkNnLOMe+olKt80v6Icbc6jEHWj6J6PkQm1uN9BwINfM8KzzIv6ep2l5cnRZmm3WV JE2d39AZuxqw5sLFWp21EVGz5ajLikXazvDXGkVmRmD7Rt91kW9djSFhE3MPSICZpDAmjh3BOZejI QVUjtt8WMukq4B2ykF/0zGz+cnHrvhwiNUCosKlOGfFIze1Es6amOOl+NLFb+P9FlrmPTsEYmzxsX aPwm+gq5LvsX//pfF9DICjI23d6KFXTd7PX3CeBZvuKAG63RZ8glYtaL3R27X1os76qQBJdeVzd6F Smfc9x/g==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=worktop.programming.kicks-ass.net) by casper.infradead.org with esmtpsa (Exim 4.94.2 #2 (Red Hat Linux)) id 1nvaV3-004Ivm-Pe; Mon, 30 May 2022 08:11:41 +0000 Received: by worktop.programming.kicks-ass.net (Postfix, from userid 1000) id 5A867980DE7; Mon, 30 May 2022 10:11:41 +0200 (CEST) Date: Mon, 30 May 2022 10:11:41 +0200 From: Peter Zijlstra To: Frederic Weisbecker Cc: Juri Lelli , Tejun Heo , Waiman Long , LKML , "Paul E . McKenney" , Paul Gortmaker , Johannes Weiner , Marcelo Tosatti , Phil Auld , Zefan Li , Daniel Bristot de Oliveira , Nicolas Saenz Julienne , rcu@vger.kernel.org Subject: Re: [RFC PATCH 4/4] cpuset: Support RCU-NOCB toggle on v2 root partitions Message-ID: References: <20220525221055.1152307-1-frederic@kernel.org> <20220525221055.1152307-5-frederic@kernel.org> <20220526225141.GA1214445@lothringen> <9e44bb00-955a-dbc6-a863-be649e0c701f@redhat.com> <20220527083018.n43nc73vuuzm5ixo@localhost.localdomain> <20220530004049.GA1251147@lothringen> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220530004049.GA1251147@lothringen> Precedence: bulk List-ID: X-Mailing-List: rcu@vger.kernel.org On Mon, May 30, 2022 at 02:40:49AM +0200, Frederic Weisbecker wrote: > On Sat, May 28, 2022 at 04:24:50PM +0200, Peter Zijlstra wrote: > > On Fri, May 27, 2022 at 10:30:18AM +0200, Juri Lelli wrote: > > > Hi, > > > > > > On 26/05/22 14:37, Tejun Heo wrote: > > > > On Thu, May 26, 2022 at 08:28:43PM -0400, Waiman Long wrote: > > > > > I am thinking along the line that it will not be hierarchical. However, > > > > > cpuset can be useful if we want to have multiple isolated partitions > > > > > underneath the top cpuset with different isolation attributes, but no more > > > > > sub-isolated partition with sub-attributes underneath them. IOW, we can only > > > > > set them at the first level under top_cpuset. Will that be useful? > > > > > > > > At that point, I'd just prefer to have it under /proc or /sys. > > > > > > FWIW, I was under the impression that this would nicely fit along the > > > side of other feaures towards implenting dynamic isolation of CPUs (say > > > https://lore.kernel.org/lkml/20220510153413.400020-1-longman@redhat.com/ > > > for example). Wouldn't be awkward to have to poke different places to > > > achieve isolation at runtime? > > > > This, that's what I was thinking. > > > > My main objection to the whole thing is that it's an RCU_NOCB specific > > interface. *That* I think is daft. > > > > I was thinking a partition would be able to designate a house-keeping > > sub-partition/mask, but who cares about all the various different > > housekeeping parties. > > It's time for the isolation users to step up here! I very rarely hear from them > and I just can't figure out by myself all the variants of uses for each of the > isolation features. May be some people are only interested in nocb for some > specific uses, or may be it never makes sense without nohz full and all the rest > of the isolation features. So for now I take the very cautious path to split the > interface. This is ABI, you can't walk back on it. I would suggest starting with an 'all feature' isolation. Only if there's real demand for something more fine-grained add that on top. Simple first etc.