Re: [Xen-devel] [PATCH] Simulates the MSIx table read operation

To:	konrad.wilk@xxxxxxxxxx
Subject:	Re: [Xen-devel] [PATCH] Simulates the MSIx table read operation
From:	Liu Yuan <yetiboy1230@xxxxxxxxx>
Date:	Wed, 11 Aug 2010 00:04:15 +0800
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
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>I am having a hard time understanding this.  Is the issue here that
>read/write of the MSI-X table is being done in QEMU, and it is much
>better to do so in the hypervisor which traps already the mask/unmaks

>operation so that QEMU is not overwhelmed by having to do this?

Yes, having QEMU do this read operation,it needs much more CPU cycles and longer latency.

[before patch]
read path: Guest -> Xen -> QEMU -> XEN -> Guest

[after patch]
read path: Guest -> Xen -> Guest

Xen traps all the MSIx table operation. And before this patch, only mask/unmask is simulated in
Xen. With this patch applied, READ will be simulated and WRITE will *still* be forwarded to QEMU.


>
>With this in patch in place, wouldn't QEMU still do the read operation?

No

Thanks,
Yuan

--
I am Multician, really

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Re: [Xen-devel] [PATCH] Simulates the MSIx table read operation