From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-bl2on0081.outbound.protection.outlook.com ([65.55.169.81]:50048 "EHLO na01-bl2-obe.outbound.protection.outlook.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753840AbcFPPjX (ORCPT ); Thu, 16 Jun 2016 11:39:23 -0400 Subject: Re: [PATCH 02/13] irq: Introduce IRQD_AFFINITY_MANAGED flag To: Christoph Hellwig References: <1465934346-20648-1-git-send-email-hch@lst.de> <1465934346-20648-3-git-send-email-hch@lst.de> <0412b942-ea0d-d4eb-c724-8243d12ff6f3@sandisk.com> <20160615102311.GA16619@lst.de> <67ef7a1c-56e1-db2c-b038-f9784fc1f52f@sandisk.com> <20160615151415.GA1919@localhost.localdomain> <7f0b16bd-b39f-99e6-c1c1-6a508bf9bbbf@sandisk.com> <20160615160316.GB1919@localhost.localdomain> <86aa652b-48d0-a7bb-683e-bf43939aa811@sandisk.com> <20160616152006.GA13615@lst.de> CC: Keith Busch , "tglx@linutronix.de" , "axboe@fb.com" , "linux-block@vger.kernel.org" , "linux-pci@vger.kernel.org" , "linux-nvme@lists.infradead.org" , "linux-kernel@vger.kernel.org" From: Bart Van Assche Message-ID: Date: Thu, 16 Jun 2016 17:39:07 +0200 MIME-Version: 1.0 In-Reply-To: <20160616152006.GA13615@lst.de> Content-Type: text/plain; charset="windows-1252"; format=flowed Sender: linux-pci-owner@vger.kernel.org List-ID: On 06/16/2016 05:20 PM, Christoph Hellwig wrote: > On Wed, Jun 15, 2016 at 09:36:54PM +0200, Bart Van Assche wrote: >> Do you agree that - ignoring other interrupt assignments - that the latter >> interrupt assignment scheme would result in higher throughput and lower >> interrupt processing latency? > > Probably. Once we've got it in the core IRQ code we can tweak the > algorithm to be optimal. Sorry but I'm afraid that we are embedding policy in the kernel, something we should not do. I know that there are workloads for which dedicating some CPU cores to interrupt processing and other CPU cores to running kernel threads improves throughput, probably because this results in less cache eviction on the CPU cores that run kernel threads and some degree of interrupt coalescing on the CPU cores that process interrupts. My concern is that I doubt that there is an interrupt assignment scheme that works optimally for all workloads. Hence my request to preserve the ability to modify interrupt affinity from user space. Bart.