From: Milton Miller <miltonm@bga.com>
To: ajm@sgi.com (Alan Mayer)
Cc: linux-kernel@vger.kernel.org
Subject: Re: irqs on large machines (patch)
Date: Wed, 25 Sep 2002 04:11:01 -0500 (CDT) [thread overview]
Message-ID: <200209250911.g8P9B1734121@sullivan.realtime.net> (raw)
In-Reply-To: <Pine.SGI.3.96.1020924142045.102141A-100000@fergus.americas.sgi.com>
PowerPC 64 (p690 in particular) had a similar but different
problem with NR_IRQS.
The hardware gives direct vectors, but the number space is 9 bits
to identify the pci host bridge in the drawers, and yet 4 more to
identify the source on the pci bus. All of the 9 bits are used at
various levels of the hardware for routing, so the global number
space is a bit sparse.
Each interrupt can be sent to the global queue or a specific
processor's queue.
Rather than size NR_IRQS for the native index, the hardware numbers
are mapped with a simple mapping table that directly maps dense
linux irqs to hardware numbers. Thus the linux NR_IRQs is set based on
the total number of hardware sources. (And yes, we found we needed
/proc/interrupts to be seq_file based, but that is long merged).
Perhaps this will give you ideas for other alternatives? This approach
could also allow you to assign IO interrupts to a node if your hardware
allows.
milton
--
[I'll look for any replys on the list]
next prev parent reply other threads:[~2002-09-25 9:05 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-09-24 19:22 irqs on large machines (patch) Alan Mayer
2002-09-25 9:11 ` Milton Miller [this message]
2002-09-25 14:35 ` Alan Mayer
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