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xen-devel
Re: [Xen-devel] [PATCh][VT] partial PIC to HV patch
On 22 Sep 2005, at 10:33, Dong, Eddie wrote:
Keir:
This is patch to move PIC mask/EOI access to HV for performance
and we saw about 5% performance increasement with this patch.
I'm not sure about this. I don't much like splitting the implementation
of a device across both Xen and qemu -- I'd rather implement entirely
within one or the other. Our eventual aim should be to move all non-Xen
device models into the context of the vmx domain (running as a paravirt
'mini domain' in rings 1 to 3 of the root vmcs). This might reduce
latency enough for most devices to avoid distasteful 'split'
device-model implementations.
In the case of local APICs, I/O APICs and the legacy PIC I can accept
that, even in the above model there will probably be a measurable
performance improvement to implementing these devices within Xen. But I
think this should be done by moving their complete implementation into
Xen and defining a clean interface to device models running in domain0
and/or rings 1-3. In the case of the PIC, this could be done by having
a virtualised 'interrupt wire' for each device (e.g., represent an
'interrupt edge' by a special call into Xen that runs the PIC device
model).
The other argument for putting the PIC and IO-APIC in Xen is that the
PIT is already there, and having it call out into a non-Xen device
model to send interrupts is rather gross.
-- Keir
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