From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031821AbeCAPPY (ORCPT ); Thu, 1 Mar 2018 10:15:24 -0500 Received: from mga06.intel.com ([134.134.136.31]:19026 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031631AbeCAPPX (ORCPT ); Thu, 1 Mar 2018 10:15:23 -0500 X-Amp-Result: UNSCANNABLE X-Amp-File-Uploaded: False X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.47,408,1515484800"; d="scan'208";a="179107974" Date: Thu, 1 Mar 2018 08:15:44 -0700 From: Keith Busch To: "jianchao.wang" Cc: Sagi Grimberg , Christoph Hellwig , axboe@fb.com, linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org Subject: Re: [PATCH V2] nvme-pci: assign separate irq vectors for adminq and ioq0 Message-ID: <20180301151544.GA17676@localhost.localdomain> References: <1519832921-13915-1-git-send-email-jianchao.w.wang@oracle.com> <20180228164726.GB16536@lst.de> <66e4ad3e-4019-13ec-94c0-e168cc1d95b4@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <66e4ad3e-4019-13ec-94c0-e168cc1d95b4@oracle.com> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 01, 2018 at 06:05:53PM +0800, jianchao.wang wrote: > When the adminq is free, ioq0 irq completion path has to invoke nvme_irq twice, one for itself, > one for adminq completion irq action. Let's be a little more careful on the terminology when referring to spec defined features: there is no such thing as "ioq0". The IO queues start at 1. The admin queue is the '0' index queue. > We are trying to save every cpu cycle across the nvme host path, why we waste nvme_irq cycles here. > If we have enough vectors, we could allocate another irq vector for adminq to avoid this. Please understand the _overwhelming_ majority of time spent for IRQ handling is the context switches. There's a reason you're not able to measure a perf difference between IOQ1 and IOQ2: the number of CPU cycles to chain a second action is negligible.