Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752331AbbGOR0A (ORCPT ); Wed, 15 Jul 2015 13:26:00 -0400 Received: from mail-pd0-f180.google.com ([209.85.192.180]:33332 "EHLO mail-pd0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751764AbbGORZ6 (ORCPT ); Wed, 15 Jul 2015 13:25:58 -0400 Message-ID: <55A697A3.3090305@kernel.dk> Date: Wed, 15 Jul 2015 11:25:55 -0600 From: Jens Axboe User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Keith Busch , Bart Van Assche CC: Thomas Gleixner , Christoph Hellwig , linux-rdma@vger.kernel.org, linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org, ksummit-discuss@lists.linuxfoundation.org Subject: Re: [Ksummit-discuss] [TECH TOPIC] IRQ affinity References: <20150715120708.GA24534@infradead.org> <55A67F11.1030709@sandisk.com> In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1988 Lines: 39 On 07/15/2015 11:19 AM, Keith Busch wrote: > On Wed, 15 Jul 2015, Bart Van Assche wrote: >> * With blk-mq and scsi-mq optimal performance can only be achieved if >> the relationship between MSI-X vector and NUMA node does not change >> over time. This is necessary to allow a blk-mq/scsi-mq driver to >> ensure that interrupts are processed on the same NUMA node as the >> node on which the data structures for a communication channel have >> been allocated. However, today there is no API that allows >> blk-mq/scsi-mq drivers and irqbalanced to exchange information >> about the relationship between MSI-X vector ranges and NUMA nodes. > > We could have low-level drivers provide blk-mq the controller's irq > associated with a particular h/w context, and the block layer can provide > the context's cpumask to irqbalance with the smp affinity hint. > > The nvme driver already uses the hwctx cpumask to set hints, but this > doesn't seems like it should be a driver responsibility. It currently > doesn't work correctly anyway with hot-cpu since blk-mq could rebalance > the h/w contexts without syncing with the low-level driver. > > If we can add this to blk-mq, one additional case to consider is if the > same interrupt vector is used with multiple h/w contexts. Blk-mq's cpu > assignment needs to be aware of this to prevent sharing a vector across > NUMA nodes. Exactly. I may have promised to do just that at the last LSF/MM conference, just haven't done it yet. The point is to share the mask, I'd ideally like to take it all the way where the driver just asks for a number of vecs through a nice API that takes care of all this. Lots of duplicated code in drivers for this these days, and it's a mess. -- Jens Axboe -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/