From owner-freebsd-current@FreeBSD.ORG Fri Nov 18 13:14:45 2011 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 2BEC9106566C for ; Fri, 18 Nov 2011 13:14:45 +0000 (UTC) (envelope-from jhb@freebsd.org) Received: from cyrus.watson.org (cyrus.watson.org [65.122.17.42]) by mx1.freebsd.org (Postfix) with ESMTP id 021088FC0A for ; Fri, 18 Nov 2011 13:14:45 +0000 (UTC) Received: from bigwig.baldwin.cx (66.111.2.69.static.nyinternet.net [66.111.2.69]) by cyrus.watson.org (Postfix) with ESMTPSA id AC9A346B23; Fri, 18 Nov 2011 08:14:44 -0500 (EST) Received: from jhbbsd.localnet (unknown [209.249.190.124]) by bigwig.baldwin.cx (Postfix) with ESMTPSA id 54BE08A052; Fri, 18 Nov 2011 08:14:44 -0500 (EST) From: John Baldwin To: Matteo Landi Date: Fri, 18 Nov 2011 08:00:06 -0500 User-Agent: KMail/1.13.5 (FreeBSD/8.2-CBSD-20110714-p8; KDE/4.5.5; amd64; ; ) References: <201111170953.58151.jhb@freebsd.org> In-Reply-To: MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201111180800.06593.jhb@freebsd.org> X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.2.6 (bigwig.baldwin.cx); Fri, 18 Nov 2011 08:14:44 -0500 (EST) Cc: freebsd-current@freebsd.org Subject: Re: ixgbe and fast interrupts X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 18 Nov 2011 13:14:45 -0000 On Friday, November 18, 2011 3:46:02 am Matteo Landi wrote: > > you probably want to be using MSI-X for a 10G NIC instead of INTx anyway. > > Why do you say that? Is MSI-X faster than INTx in terms of interrupt > latency? When should I use MSI-X, instead of fast filters interrupts > (fast interrupt?), instead of ithread interrupts? Thanks in advace. With MSI-X you can have more than one interrupt and those interrupts can be distributed across CPUs. This means you can (somewhat) tie each queue on your NIC to a different CPU. MSI-X vs INTx is orthogonal to fast vs filter, but in general MSI and MSI-X interrupts are not shared, and require no interrupt masking in hardware (they are effectively edge-triggered), so using a filter for MSI is rather pointless and only adds needless complexity. For MSI I would just use a theraded interrupt handler. For INTx, I would only use a fast interrupt handler if there is a really good reason to do so (e.g. em(4) does so to work around broken Intel Host-PCI bridges). -- John Baldwin