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Subject: Re: [patch] oprofile + ppc750cx perfmon
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: Bryan Rittmeyer <bryanr@bryanr.org>
Cc: oprofile-list@lists.sourceforge.net, linux-kernel@vger.kernel.org,
       linuxppc-dev@lists.linuxppc.org
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On Tue, 2003-03-25 at 09:57, Bryan Rittmeyer wrote:

> wow. inside of open_pic.c, I bet it's code like this
> 
>         while (openpic_read(addr) & OPENPIC_ACTIVITY);
> 
> that's showing up.

That's interesting. You are raising again an old debate of
wether to disable the IRQ during handling on openpic or not,
I beleive we don't need to disable it on this PIC, but we
do this for "safety" reasons.

In fact, I think our

openpic_ack_irq() should do something like

  if (edge)
	openpic_eoi();

and our openpic_end_irq() something like

  if (level)
	openpic_eoi();

Also, the fact that PIC access is slow is a generic "feature"
of such chips, I also think we could actually be smarter and only
soft-disable IRQs with a flag in the descriptor, and hard disable
them if and only if they actually occur while disabled.

Ben.

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