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Re: [Xen-devel] [PATCH v2] x86/hvm: re-work viridian APIC assist code
- To: Paul Durrant <Paul.Durrant@xxxxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: David Woodhouse <dwmw2@xxxxxxxxxxxxx>
- Date: Wed, 05 Sep 2018 11:45:00 +0100
- Cc: Eslam Elnikety <elnikety@xxxxxxxxx>, Andrew Cooper <Andrew.Cooper3@xxxxxxxxxx>, Shan Haitao <haitao.shan@xxxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>
- Delivery-date: Wed, 05 Sep 2018 10:45:12 +0000
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- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, 2018-09-05 at 10:40 +0000, Paul Durrant wrote:
>
> Actually the neatest approach would be to get information into the
> vlapic code as to whether APIC assist is suitable for the given
> vector so that the code there can selectively enable it, and then Xen
> would know it was safe to avoid fully emulating an EOI for anything
> that did have assist enabled.
I'm not sure I understand why an assisted EOI should be any different
from "normal" EOI.
The global lock and indirect function calls and all that stuff that
hvm_dpci_msi_eoi() does are *expensive*, for a rare case.
Why not bypass all that when it's not needed, for "normal" EOI and
APIC-assisted EOI alike? Why have a distinction between the two? Attachment:
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