From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:16374 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753154AbcFONJl (ORCPT ); Wed, 15 Jun 2016 09:09:41 -0400 Received: from pps.filterd (m0098404.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.11/8.16.0.11) with SMTP id u5FD4XZr036661 for ; Wed, 15 Jun 2016 09:09:41 -0400 Received: from e24smtp05.br.ibm.com (e24smtp05.br.ibm.com [32.104.18.26]) by mx0a-001b2d01.pphosted.com with ESMTP id 23jfmpwnct-1 (version=TLSv1.2 cipher=AES256-SHA bits=256 verify=NOT) for ; Wed, 15 Jun 2016 09:09:41 -0400 Received: from localhost by e24smtp05.br.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 15 Jun 2016 10:09:38 -0300 Subject: Re: [PATCH 06/13] irq: add a helper spread an affinity mask for MSI/MSI-X vectors To: Christoph Hellwig References: <1465934346-20648-1-git-send-email-hch@lst.de> <1465934346-20648-7-git-send-email-hch@lst.de> <57607D0E.1060907@linux.vnet.ibm.com> <20160615101045.GB16425@lst.de> Cc: linux-block@vger.kernel.org, linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org, axboe@fb.com, tglx@linutronix.de, bart.vanassche@sandisk.com From: "Guilherme G. Piccoli" Date: Wed, 15 Jun 2016 10:09:33 -0300 MIME-Version: 1.0 In-Reply-To: <20160615101045.GB16425@lst.de> Content-Type: text/plain; charset=windows-1252; format=flowed Message-Id: <5761538D.6060303@linux.vnet.ibm.com> Sender: linux-pci-owner@vger.kernel.org List-ID: Thanks for the responses Bart and Christoph. On 06/15/2016 07:10 AM, Christoph Hellwig wrote: > On Tue, Jun 14, 2016 at 06:54:22PM -0300, Guilherme G. Piccoli wrote: >> On 06/14/2016 04:58 PM, Christoph Hellwig wrote: >>> This is lifted from the blk-mq code and adopted to use the affinity mask >>> concept just intruced in the irq handling code. >> >> Very nice patch Christoph, thanks. There's a little typo above, on >> "intruced". > > fixed. > >> Another little typo above in "assining". > > fixed a swell. > >> I take this opportunity to ask you something, since I'm working in a >> related code in a specific driver > > Which driver? One of the points here is to get this sort of code out > of drivers and into common code.. A network driver, i40e. I'd be glad to implement/see some common code to raise the topology information I need, but I was implementing on i40e more as a test case/toy example heheh... >> - sorry in advance if my question is >> silly or if I misunderstood your code. >> >> The function irq_create_affinity_mask() below deals with the case in which >> we have nr_vecs < num_online_cpus(); in this case, wouldn't be a good idea >> to trying distribute the vecs among cores? >> >> Example: if we have 128 online cpus, 8 per core (meaning 16 cores) and 64 >> vecs, I guess would be ideal to distribute 4 vecs _per core_, leaving 4 >> CPUs in each core without vecs. > > There have been some reports about the blk-mq IRQ distribution being > suboptimal, but no one sent patches so far. This patch just moves the > existing algorithm into the core code to be better bisectable. > > I think an algorithm that takes cores into account instead of just SMT > sibling would be very useful. So if you have a case where this helps > for you an incremental patch (or even one against the current blk-mq > code for now) would be appreciated. ...but now I'll focus on the common/general case! Thanks for the suggestion Christoph. I guess would be even better to have a generic function that retrieves an optimal mask, something like topology_get_optimal_mask(n, *cpumask), in which we get the best distribution of n CPUs among all cores and return such a mask - interesting case is when n < num_online_cpus. So, this function could be used inside your irq_create_affinity_mask() and maybe in other places it is needed. I was planning to use topology_core_id() to retrieve the core of a CPU, if anybody has a better idea, I'd be glad to hear it. Cheers, Guilherme > > _______________________________________________ > Linux-nvme mailing list > Linux-nvme@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-nvme >