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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=unavailable 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 2078EC282D9 for ; Thu, 31 Jan 2019 23:41:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id F0B1D2086C for ; Thu, 31 Jan 2019 23:41:42 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727971AbfAaXll (ORCPT ); Thu, 31 Jan 2019 18:41:41 -0500 Received: from ale.deltatee.com ([207.54.116.67]:52234 "EHLO ale.deltatee.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726135AbfAaXll (ORCPT ); Thu, 31 Jan 2019 18:41:41 -0500 Received: from guinness.priv.deltatee.com ([172.16.1.162]) by ale.deltatee.com with esmtp (Exim 4.89) (envelope-from ) id 1gpLxe-0005g7-UT; Thu, 31 Jan 2019 16:41:35 -0700 To: Dave Jiang , linux-kernel@vger.kernel.org, linux-ntb@googlegroups.com, linux-pci@vger.kernel.org, iommu@lists.linux-foundation.org, linux-kselftest@vger.kernel.org, Jon Mason , Bjorn Helgaas , Joerg Roedel Cc: Allen Hubbe , Serge Semin , Eric Pilmore References: <20190131185656.17972-1-logang@deltatee.com> <345197a6-89e6-c0de-5f7b-a646b5f396c9@intel.com> <29f7e3fe-5354-6156-1243-7248ffb2249f@deltatee.com> <7e3eed52-8e3a-c472-392a-5dc5689290ae@intel.com> From: Logan Gunthorpe Message-ID: <5f8b1616-a005-7658-978f-16466fcc3886@deltatee.com> Date: Thu, 31 Jan 2019 16:41:32 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <7e3eed52-8e3a-c472-392a-5dc5689290ae@intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 7bit X-SA-Exim-Connect-IP: 172.16.1.162 X-SA-Exim-Rcpt-To: epilmore@gigaio.com, fancer.lancer@gmail.com, allenbh@gmail.com, joro@8bytes.org, bhelgaas@google.com, jdmason@kudzu.us, linux-kselftest@vger.kernel.org, iommu@lists.linux-foundation.org, linux-pci@vger.kernel.org, linux-ntb@googlegroups.com, linux-kernel@vger.kernel.org, dave.jiang@intel.com X-SA-Exim-Mail-From: logang@deltatee.com Subject: Re: [PATCH 0/9] Support using MSI interrupts in ntb_transport X-SA-Exim-Version: 4.2.1 (built Tue, 02 Aug 2016 21:08:31 +0000) X-SA-Exim-Scanned: Yes (on ale.deltatee.com) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019-01-31 3:46 p.m., Dave Jiang wrote: > I believe irqbalance writes to the file /proc/irq/N/smp_affinity. So > maybe take a look at the code that starts from there and see if it would > have any impact on your stuff. Ok, well on my system I can write to the smp_affinity all day and the MSI interrupts still work fine. The MSI code is a bit difficult to trace and audit with all the different chips and the parent chips which I don't have a good understanding of. But I can definitely see that it could be possible for some chips to change the address as smp_affinitiy will eventually sometimes call msi_domain_set_affinity() which does seem to recompose the message and write it back to the chip. So, I could relatively easily add a callback to msi_desc to catch this and resend the MSI address/data. However, I'm not sure how this is ever done atomically. It seems like there would be a race while the device updates its address where old interrupts could be triggered. This race would be much longer for us when sending this information over the NTB link. Though, I guess if the only change is that it encodes CPU information in the address then that would not be an issue. However, I'm not sure I can say that for certain without a comprehensive understanding of all the IRQ chips. Any thoughts on this? Logan