From mboxrd@z Thu Jan 1 00:00:00 1970 From: Kashyap Desai Subject: RE: [LSF/MM TOPIC] irq affinity handling for high CPU count machines Date: Fri, 2 Feb 2018 14:19:01 +0530 Message-ID: <6754a4c3ed7e1f1ea5473bd97625aa51@mail.gmail.com> References: <45dc032d-a0ce-816c-d2c5-74c69433bd29@suse.de> <20180201150532.GA31930@ming.t460p> <0f650f4b-aa7f-bf52-2ecb-582761b4937f@suse.de> <20180202020235.GE19173@ming.t460p> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: Received: from mail-io0-f172.google.com ([209.85.223.172]:35801 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750871AbeBBItE (ORCPT ); Fri, 2 Feb 2018 03:49:04 -0500 Received: by mail-io0-f172.google.com with SMTP id m11so22205854iob.2 for ; Fri, 02 Feb 2018 00:49:03 -0800 (PST) In-Reply-To: <20180202020235.GE19173@ming.t460p> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Ming Lei Cc: Hannes Reinecke , lsf-pc@lists.linux-foundation.org, "linux-scsi@vger.kernel.org" , linux-nvme@lists.infradead.org > > > > Today I am looking at one megaraid_sas related issue, and found > > > > pci_alloc_irq_vectors(PCI_IRQ_AFFINITY) is used in the driver, so > > > > looks each reply queue has been handled by more than one CPU if > > > > there are more CPUs than MSIx vectors in the system, which is done > > > > by generic irq affinity code, please see kernel/irq/affinity.c. > > > > Yes. That is a problematic area. If CPU and MSI-x(reply queue) is 1:1 > > mapped, we don't have any issue. > > I guess the problematic area is similar with the following link: > > https://marc.info/?l=linux-kernel&m=151748144730409&w=2 Hi Ming, Above mentioned link is different discussion and looks like a generic issue. megaraid_sas/mpt3sas will have same symptoms if irq affinity has only offline CPUs. Just for info - "In such condition, we can ask users to disable affinity hit via module parameter " smp_affinity_enable". > > otherwise could you explain a bit about the area? Please check below post for more details. https://marc.info/?l=linux-scsi&m=151601833418346&w=2