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From: Paul Brook <paul@codesourcery.com>
Subject: Re: [Qemu-devel] Re: [PATCH 0/4] pci: interrupt status/interrupt
	disable support
Date: Thu, 26 Nov 2009 12:41:03 +0000
References: <20091125165834.GA24783@redhat.com>
	<20091126032146.GH25483%yamahata@valinux.co.jp>
	<20091126094811.GB26861@redhat.com>
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To: qemu-devel@nongnu.org
Cc: Isaku Yamahata <yamahata@valinux.co.jp>, "Michael S. Tsirkin" <mst@redhat.com>

> No, this would slow us down because these are per-pin.
> We need a sum of interrupts so that config space
> can be updated by a single command.
> Interrupts are a fastpath, extra loops there should be avoided.

It's really not that much of a fast path. Unless you're doing something 
particularly obscure then even under heavy load you're unlikely to exceed a 
few kHz.  Compared to the average PIC implementation, and the overhead of the 
actual CPU interrupt, I find it hard to believe that looping over precisely 4 
entries has any real performance hit.

Paul