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From: Milton Miller <>
To: (Alan Mayer)
Subject: Re: irqs on large machines (patch)
Date: Wed, 25 Sep 2002 04:11:01 -0500 (CDT)	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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

[I'll look for any replys on the list]

  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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