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RE: [Xen-devel] [Patch] x86: enforce strict memory order for x2apic

To: 'Keir Fraser' <keir.fraser@xxxxxxxxxxxxx>, 'Jan Beulich' <jbeulich@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject: RE: [Xen-devel] [Patch] x86: enforce strict memory order for x2apic
From: "Tian, Kevin" <kevin.tian@xxxxxxxxx>
Date: Thu, 25 Sep 2008 16:38:42 +0800
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Thread-topic: [Xen-devel] [Patch] x86: enforce strict memory order for x2apic
>From: Keir Fraser [mailto:keir.fraser@xxxxxxxxxxxxx]
>Sent: 2008年9月25日 16:36
>On 25/9/08 09:29, "Tian, Kevin" <kevin.tian@xxxxxxxxx> wrote:
>>> On the other hand you're penalizing LAPIC systems with
>this, too. I'm
>>> not certain that's better than fixing the (incorrect)
>>> assumptions just in
>>> the x2APIC case.
>> I agree. I'll revise the patch to add a 'mb()' in x2APIC instead,
>> though that may bring a bit overhead to cases when fencing
>> is not required, like event check IPI.
>To be precise, mb() at top of send_IPI_mask_x2apic(), and
>wmb() may as well
>go from on_selected_cpus() as we can assume send_IPI_mask() is
>a barrier.
>I'll do the patch for this myself.

Yes, and thanks. Also please add a wmb() in flush_area_mask,
though it's a nop but semanticly desired like for on_selected_cpus.

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