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=-15.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 9287FC48BDF for ; Tue, 15 Jun 2021 20:04:49 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6F24F613C2 for ; Tue, 15 Jun 2021 20:04:49 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230081AbhFOUGw (ORCPT ); Tue, 15 Jun 2021 16:06:52 -0400 Received: from verein.lst.de ([213.95.11.211]:51041 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229931AbhFOUGw (ORCPT ); Tue, 15 Jun 2021 16:06:52 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id AA58368B05; Tue, 15 Jun 2021 22:04:43 +0200 (CEST) Date: Tue, 15 Jun 2021 22:04:43 +0200 From: Christoph Hellwig To: Bjorn Helgaas Cc: Thomas Gleixner , LKML , Ming Lei , Christoph Hellwig , Jens Axboe , linux-block@vger.kernel.org, Sagi Grimberg , linux-nvme@lists.infradead.org, linux-pci@vger.kernel.org, Keith Busch , Marc Zyngier , Sumit Saxena , Kashyap Desai , Shivasharan Srikanteshwara Subject: Re: [patch v6 3/7] genirq/affinity: Add new callback for (re)calculating interrupt sets Message-ID: <20210615200443.GA6557@lst.de> References: <20190216172228.512444498@linutronix.de> <20210615195707.GA2909907@bjorn-Precision-5520> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210615195707.GA2909907@bjorn-Precision-5520> User-Agent: Mutt/1.5.17 (2007-11-01) Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On Tue, Jun 15, 2021 at 02:57:07PM -0500, Bjorn Helgaas wrote: > On Sat, Feb 16, 2019 at 06:13:09PM +0100, Thomas Gleixner wrote: > > From: Ming Lei > > > > The interrupt affinity spreading mechanism supports to spread out > > affinities for one or more interrupt sets. A interrupt set contains one or > > more interrupts. Each set is mapped to a specific functionality of a > > device, e.g. general I/O queues and read I/O queus of multiqueue block > > devices. > > > > The number of interrupts per set is defined by the driver. It depends on > > the total number of available interrupts for the device, which is > > determined by the PCI capabilites and the availability of underlying CPU > > resources, and the number of queues which the device provides and the > > driver wants to instantiate. > > > > The driver passes initial configuration for the interrupt allocation via a > > pointer to struct irq_affinity. > > > > Right now the allocation mechanism is complex as it requires to have a loop > > in the driver to determine the maximum number of interrupts which are > > provided by the PCI capabilities and the underlying CPU resources. This > > loop would have to be replicated in every driver which wants to utilize > > this mechanism. That's unwanted code duplication and error prone. > > > > In order to move this into generic facilities it is required to have a > > mechanism, which allows the recalculation of the interrupt sets and their > > size, in the core code. As the core code does not have any knowledge about the > > underlying device, a driver specific callback is required in struct > > irq_affinity, which can be invoked by the core code. The callback gets the > > number of available interupts as an argument, so the driver can calculate the > > corresponding number and size of interrupt sets. > > > > At the moment the struct irq_affinity pointer which is handed in from the > > driver and passed through to several core functions is marked 'const', but for > > the callback to be able to modify the data in the struct it's required to > > remove the 'const' qualifier. > > > > Add the optional callback to struct irq_affinity, which allows drivers to > > recalculate the number and size of interrupt sets and remove the 'const' > > qualifier. > > > > For simple invocations, which do not supply a callback, a default callback > > is installed, which just sets nr_sets to 1 and transfers the number of > > spreadable vectors to the set_size array at index 0. > > > > This is for now guarded by a check for nr_sets != 0 to keep the NVME driver > > working until it is converted to the callback mechanism. > > > > To make sure that the driver configuration is correct under all circumstances > > the callback is invoked even when there are no interrupts for queues left, > > i.e. the pre/post requirements already exhaust the numner of available > > interrupts. > > > > At the PCI layer irq_create_affinity_masks() has to be invoked even for the > > case where the legacy interrupt is used. That ensures that the callback is > > invoked and the device driver can adjust to that situation. > > > > [ tglx: Fixed the simple case (no sets required). Moved the sanity check > > for nr_sets after the invocation of the callback so it catches > > broken drivers. Fixed the kernel doc comments for struct > > irq_affinity and de-'This patch'-ed the changelog ] > > > > Signed-off-by: Ming Lei > > Signed-off-by: Thomas Gleixner > > > @@ -1196,6 +1196,13 @@ int pci_alloc_irq_vectors_affinity(struc > > /* use legacy irq if allowed */ > > if (flags & PCI_IRQ_LEGACY) { > > if (min_vecs == 1 && dev->irq) { > > + /* > > + * Invoke the affinity spreading logic to ensure that > > + * the device driver can adjust queue configuration > > + * for the single interrupt case. > > + */ > > + if (affd) > > + irq_create_affinity_masks(1, affd); > > This looks like a leak because irq_create_affinity_masks() returns a > pointer to kcalloc()ed space, but we throw away the pointer. > > Or is there something very subtle going on here, like this special > case doesn't allocate anything? I do see the "Nothing to assign?" > case that returns NULL with no alloc, but it's not completely trivial > to verify that we take that case here. > > > pci_intx(dev, 1); > > return 1; > > } ---end quoted text---