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[Xen-devel] Re: [PATCH] Allocate vmcs pages when system booting

To: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH] Allocate vmcs pages when system booting
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Thu, 12 Nov 2009 15:04:02 +0000
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On 12/11/2009 14:58, "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx> wrote:

>> Can you try this alternative fix please?
> Yes, spin_debug_disable() is the first idea come into my mind, I change my
> mind because the spin_debug is a global variable.  disable spin_debug() before
> start_secondary means maybe we can't catch error happens at that window, so I
> choose this method. Previously I thought high-end system support cpu hotplug
> may not care about the 64 pages :$

CONFIG_HOTPLUG_CPU is not a user-accessible build option. In fact manually
disabling it in config.h resulted in a broken build, and now I basically
stripped out the non-HOTPLUG_CPU code (in c/s 20431). So this would be an
overhead for absolutely everyone.

> Or you assume this window is quite small, and we can assume safely if a error
> happening at this window, it will happen in other timeslot in the end,
> sepecially this function itself don't need the check?

Exactly. The spinlock debug checking can be best effort. I did think about
allowing the checks to be disabled per-cpu, but I don't think it's worth it.

I will check in my suggested fix, then.

 -- Keir

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