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Date: Fri, 04 May 2007 18:45:58 -0700
From: "Michael Chan" <mchan@...adcom.com>
To: "Jeff Garzik" <jeff@...zik.org>
cc: "David Miller" <davem@...emloft.net>,
"netdev" <netdev@...r.kernel.org>
Subject: Re: [PATCH 10/11][TG3]: Reduce spurious interrupts.
On Fri, 2007-05-04 at 20:42 -0400, Jeff Garzik wrote:
> Michael Chan wrote:
> > [TG3]: Reduce spurious interrupts.
> >
> > Spurious interrupts are often encountered especially on systems
> > using the 8259 PIC mode. This is because the I/O write to deassert
> > the interrupt is posted and won't get to the chip immediately. As
> > a result, the IRQ may remain asserted after the IRQ handler exits,
> > causing spurious interrupts.
> >
> > An unconditional read to flush the I/O write to force the IRQ to de-
> > assert immediately is not desirable because it impacts performance in
> > the fast path. So we only do this after we have some indications of
> > spurious interrupts.
> >
> > Signed-off-by: Michael Chan <mchan@...adcom.com>
>
> hmmmm, this is a bit questionable that it needs to be here.
>
> I think it's just a fact of life that it is important to flush certain
> writes...
>
> I'm not sure a driver needs to be adding code to avoid the obvious
> solution. It would be annoying if all drivers had code to do this.
We had a discussion about 2 years ago and David decided to remove the
I/O read to improve performance. Since then a small number of users
have been complaining about spurious interrupts. We can add back the
unconditional read or do this detection thing which I agree is somewhat
annoying. David, what do you think?
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