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[Xen-devel] Re: [patch 13/26] Xen-paravirt_ops: Consistently wrap paravirt ops callsites to make them patchable
- To: Zachary Amsden <zach@xxxxxxxxxx>
- From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Date: Tue, 20 Mar 2007 19:15:15 -0700 (PDT)
- Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx, akpm@xxxxxxxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxx, netdev@xxxxxxxxxxxxxxx, Rusty Russell <rusty@xxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx, chrisw@xxxxxxxxxxxx, Andi Kleen <ak@xxxxxx>, "Eric W. Biederman" <ebiederm@xxxxxxxxxxxx>, anthony@xxxxxxxxxxxxx, mingo@xxxxxxx, David Miller <davem@xxxxxxxxxxxxx>
- Delivery-date: Wed, 21 Mar 2007 02:29:45 -0700
- List-id: Xen developer discussion <xen-devel.lists.xensource.com>
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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