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4180bf1b65
Using hypercall to send IPIs by one vmexit instead of one by one for
xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster
mode. Intel guest can enter x2apic cluster mode when interrupt remmaping
is enabled in qemu, however, latest AMD EPYC still just supports xapic
mode which can get great improvement by Exit-less IPIs. This patchset
lets a guest send multicast IPIs, with at most 128 destinations per
hypercall in 64-bit mode and 64 vCPUs per hypercall in 32-bit mode.
Hardware: Xeon Skylake 2.5GHz, 2 sockets, 40 cores, 80 threads, the VM
is 80 vCPUs, IPI microbenchmark(https://lkml.org/lkml/2017/12/19/141):
x2apic cluster mode, vanilla
Dry-run: 0, 2392199 ns
Self-IPI: 6907514, 15027589 ns
Normal IPI: 223910476, 251301666 ns
Broadcast IPI: 0, 9282161150 ns
Broadcast lock: 0, 8812934104 ns
x2apic cluster mode, pv-ipi
Dry-run: 0, 2449341 ns
Self-IPI: 6720360, 15028732 ns
Normal IPI: 228643307, 255708477 ns
Broadcast IPI: 0, 7572293590 ns => 22% performance boost
Broadcast lock: 0, 8316124651 ns
x2apic physical mode, vanilla
Dry-run: 0, 3135933 ns
Self-IPI:
|
||
|---|---|---|
| .. | ||
| acpi | ||
| asm-generic | ||
| clocksource | ||
| crypto | ||
| drm | ||
| dt-bindings | ||
| keys | ||
| kvm | ||
| linux | ||
| math-emu | ||
| media | ||
| memory | ||
| misc | ||
| net | ||
| pcmcia | ||
| ras | ||
| rdma | ||
| scsi | ||
| soc | ||
| sound | ||
| target | ||
| trace | ||
| uapi | ||
| video | ||
| xen | ||