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 X-Spam-Level: X-Spam-Status: No, score=-3.9 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 62D60C4363A for ; Tue, 20 Oct 2020 13:42:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0DCEF22258 for ; Tue, 20 Oct 2020 13:42:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="xkc15xWP" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2407598AbgJTNl7 (ORCPT ); Tue, 20 Oct 2020 09:41:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60808 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2407501AbgJTNl6 (ORCPT ); Tue, 20 Oct 2020 09:41:58 -0400 Received: from merlin.infradead.org (merlin.infradead.org [IPv6:2001:8b0:10b:1231::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id AAF67C061755; Tue, 20 Oct 2020 06:41:57 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=merlin.20170209; h=In-Reply-To:Content-Transfer-Encoding: Content-Type:MIME-Version:References:Message-ID:Subject:Cc:To:From:Date: Sender:Reply-To:Content-ID:Content-Description; bh=4vW5VXilK7EsyfO4dPaDcP262lkk9u9nP43QqAXpv9o=; b=xkc15xWP2oUKBp63sflEvxBDBa Cpz/U6a/YNxBc/GNqwflCrTWWfEnyhrLvKzVxy+FNRknLqEYUNB6RhdwWPKMlvpQ4xg7JJ/XkBilo q7QUjhv/WsWPwJYdXhdtx4Lc9qd+kJFDDpNK43AiN9vO3W9DwLBNGGD8Utslryom4kWhPhxq9EPIL BnLhrFaS/HluTGI3ucPrvi3dw9glxbYSgWze+TZEVpJFl0jRmBuSUzCD+61w4HQG0vtlthLswWD2P DQGya+IzO4qKZq3IEzmvSILgNefksN9ddf4HKEg8Um06/WO2s6mSuXXZ5C9rOnnBV1n6U4WzsDQxO 41v7xSXw==; Received: from j217100.upc-j.chello.nl ([24.132.217.100] helo=noisy.programming.kicks-ass.net) by merlin.infradead.org with esmtpsa (Exim 4.92.3 #3 (Red Hat Linux)) id 1kUrtL-00034B-NM; Tue, 20 Oct 2020 13:41:31 +0000 Received: from hirez.programming.kicks-ass.net (hirez.programming.kicks-ass.net [192.168.1.225]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by noisy.programming.kicks-ass.net (Postfix) with ESMTPS id 964AC304D28; Tue, 20 Oct 2020 15:41:28 +0200 (CEST) Received: by hirez.programming.kicks-ass.net (Postfix, from userid 1000) id 6C545203280A1; Tue, 20 Oct 2020 15:41:28 +0200 (CEST) Date: Tue, 20 Oct 2020 15:41:28 +0200 From: Peter Zijlstra To: Nitesh Narayan Lal Cc: Marcelo Tosatti , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, linux-pci@vger.kernel.org, intel-wired-lan@lists.osuosl.org, frederic@kernel.org, sassmann@redhat.com, jesse.brandeburg@intel.com, lihong.yang@intel.com, helgaas@kernel.org, jeffrey.t.kirsher@intel.com, jacob.e.keller@intel.com, jlelli@redhat.com, hch@infradead.org, bhelgaas@google.com, mike.marciniszyn@intel.com, dennis.dalessandro@intel.com, thomas.lendacky@amd.com, jiri@nvidia.com, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, lgoncalv@redhat.com Subject: Re: [PATCH v4 4/4] PCI: Limit pci_alloc_irq_vectors() to housekeeping CPUs Message-ID: <20201020134128.GT2628@hirez.programming.kicks-ass.net> References: <20200928183529.471328-1-nitesh@redhat.com> <20200928183529.471328-5-nitesh@redhat.com> <20201016122046.GP2611@hirez.programming.kicks-ass.net> <79f382a7-883d-ff42-394d-ec4ce81fed6a@redhat.com> <20201019111137.GL2628@hirez.programming.kicks-ass.net> <20201019140005.GB17287@fuller.cnet> <20201020073055.GY2611@hirez.programming.kicks-ass.net> <078e659e-d151-5bc2-a7dd-fe0070267cb3@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable In-Reply-To: <078e659e-d151-5bc2-a7dd-fe0070267cb3@redhat.com> Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Tue, Oct 20, 2020 at 09:00:01AM -0400, Nitesh Narayan Lal wrote: >=20 > On 10/20/20 3:30 AM, Peter Zijlstra wrote: > > On Mon, Oct 19, 2020 at 11:00:05AM -0300, Marcelo Tosatti wrote: > >>> So I think it is important to figure out what that driver really wants > >>> in the nohz_full case. If it wants to retain N interrupts per CPU, and > >>> only reduce the number of CPUs, the proposed interface is wrong. > >> It wants N interrupts per non-isolated (AKA housekeeping) CPU. > > Then the patch is wrong and the interface needs changing from @min_vecs, > > @max_vecs to something that expresses the N*nr_cpus relation. >=20 > Reading Marcelo's comment again I think what is really expected is 1 > interrupt per non-isolated (housekeeping) CPU (not N interrupts). Then what is the point of them asking for N*nr_cpus when there is no isolation? Either everybody wants 1 interrupts per CPU and we can do the clamp unconditionally, in which case we should go fix this user, or they want multiple per cpu and we should go fix the interface. It cannot be both.