Date: Fri, 18 Nov 2011 08:00:06 -0500 From: John Baldwin <jhb@freebsd.org> To: Matteo Landi <matteo@matteolandi.net> Cc: freebsd-current@freebsd.org Subject: Re: ixgbe and fast interrupts Message-ID: <201111180800.06593.jhb@freebsd.org> In-Reply-To: <CALJ8J_HZiJfh_id%2BggaYZpU5UhUjZy==CK9jmdR4pePjfi=2gw@mail.gmail.com> References: <CALJ8J_HPZewO12uanb=kctQYwepMssr63E0DQh9CqV6PGaC=JA@mail.gmail.com> <201111170953.58151.jhb@freebsd.org> <CALJ8J_HZiJfh_id%2BggaYZpU5UhUjZy==CK9jmdR4pePjfi=2gw@mail.gmail.com>
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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
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