netdev - Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable

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Date:	Tue, 20 Mar 2007 19:15:15 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Zachary Amsden <zach@...are.com>
cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Rusty Russell <rusty@...tcorp.com.au>, Andi Kleen <ak@....de>,
	David Miller <davem@...emloft.net>, mingo@...e.hu,
	akpm@...ux-foundation.org, linux-kernel@...r.kernel.org,
	virtualization@...ts.osdl.org, xen-devel@...ts.xensource.com,
	chrisw@...s-sol.org, anthony@...emonkey.ws, netdev@...r.kernel.org
Subject: Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops
 callsites to make them patchable



On Tue, 20 Mar 2007, Zachary Amsden wrote:
> 
> Actually, I was thinking the irq handlers would just not mess around with
> eflags on the stack, just call the chip to ack the interrupt and re-enable
> hardware interrupts when they left, since that is free anyway with the iret.

No can do. Think level-triggered. You *need* to disable the interrupt, and 
disabling it at the CPU is the easiest approach. Even so, you need to 
worry about SMP and screaming interrupts at all CPU's, but if you don't 
ack it to the IO-APIC until later, that should be ok (alternatively, you 
need to just mask-and-ack the irq controller).

> Maybe leaving irqs disabled is better.

One of the advantages of doing that is that you only ever have a queue of 
one single entry, which then makes it easier to do the replay.

		Linus
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