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Re: [Xen-devel] Question about evtchn_callback reentry

To: Keir Fraser <keir@xxxxxxxxxxxxx>, "Xu, Anthony" <anthony.xu@xxxxxxxxx>
Subject: Re: [Xen-devel] Question about evtchn_callback reentry
From: Keir Fraser <keir@xxxxxxxxxxxxx>
Date: Mon, 18 Dec 2006 13:42:19 +0000
Cc: xen-devel@xxxxxxxxxxxxxxxxxxx, xen-ia64-devel <xen-ia64-devel@xxxxxxxxxxxxxxxxxxx>
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Thread-topic: [Xen-devel] Question about evtchn_callback reentry
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On 18/12/06 11:24, "Keir Fraser" <keir@xxxxxxxxxxxxx> wrote:

>> If evtchn_callback reentry is allowed.
>> There are 1024 event channels.
>> In theory, dom0 kernal stack may be overflowed.
>> Is there any mechanism to prevent this?
> When running natively there are over 200 vectors available for allocation to
> interrupt sources. In theory the kernel stack may be overflowed, and there
> is no mechanism in Linux to prevent this.

Okay, so I remember now that of course the APIC divides these into 16
priority levels so that does rather restrict the maximum nesting. I'll be
happy to consider adding prioritisation (or just complete disallow of
nesting) for 3.0.5. But I think you should also work to understand the root
cause of the performance drop on ia64.

 -- Keir

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