linux-kernel - RE: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table

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Message-ID: <08FE5CC30C9A3F41BF819A502CF7BF6EF98580@fmsmsx411.amr.corp.intel.com>
Date:	Tue, 27 Mar 2007 14:43:55 -0700
From:	"Williams, Mitch A" <mitch.a.williams@...el.com>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	"Grant Grundler" <grundler@...isc-linux.org>,
	<linux-pci@...ey.karlin.mff.cuni.cz>, <gregkh@...e.de>,
	<linux-kernel@...r.kernel.org>, <akpm@...ux-foundation.org>,
	"Kok, Auke-jan H" <auke-jan.h.kok@...el.com>
Subject: RE: [PATCH 2.6.21-rc5] MSI: read-flush MSI-X table

Eric W. Biederman wrote:

>> However the mask function is called at EVERY interrupt,
>> so this change would be VERY expensive.
>
>If true I think that would be bad.  However I don't see it.
>Where in handle_edge_irq do we mask the interrupt?
>The only place I see us calling ->mask is from move_native_irq
>and that only if IRQ_MOVE_PENDING is true.
>
>All I can see is us routinely calling is ack_APIC_edge.

Doh!  I was reading the code wrong.  We only mask if we're still
handling a previous interrupt on the same vector.  My bad.

However, I can't really see where mask() is used outside of that
instance.  Which then leads us back to the question:  do we need
a read flush on mask/unmask or just enable/disable?

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