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Subject[RFC PATCH] Use vAPIC when doing IPI for PVHVM guests.
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Hey,

I was running some tools in which we would heavily do rescheduling
of events - and realized to my surprise that the event channels (and
the hypercall) would slow things down. If I used the vAPIC with its
IPI support (so no VMEXIT) I got much much better performance.

Now this is an RFC because:
1). I hadn't verified from the xentrace how much less VMEXITS we get.
But I remember Boris's patches and they gave at least 10%.
I think this will get the same performance or even better.

2). I don't know what to do with migration. That is if the guest
migrates to older hardware it needs to recheck this I presume?

3). Should this be enabled by default? I did get better performance
but that was synthetic.

Thoughts?


Documentation/kernel-parameters.txt | 15 +++++------
arch/x86/xen/enlighten.c | 50 +++++++++++++++++++++++++++++++++----
arch/x86/xen/smp.c | 22 ++++++++++++++--
arch/x86/xen/spinlock.c | 18 ++++---------
arch/x86/xen/xen-ops.h | 4 +++
5 files changed, 82 insertions(+), 27 deletions(-)

Konrad Rzeszutek Wilk (2):
xen/apic: Use vAPIC for IPI if the hardware supports it.
xen_nopv: Combine a bunch of the PV features that can be disabled



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