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All of the irqfds would to be updated when update the irq
routing, it's too expensive if there're too many irqfds.
However we can reduce the cost by avoid some unnecessary
updates. For irqs of MSI type on X86, the update can be
saved if the msi values are not change.
The vfio migration could receives benefit from this optimi-
zaiton. The test VM has 128 vcpus and 8 VF (with 65 vectors
enabled), so the VM has more than 520 irqfds. We mesure the
cost of the vfio_msix_enable (in QEMU, it would set routing
for each irqfd) for each VF, and we can see the total cost
can be significantly reduced.
Origin Apply this Patch
1st 8 4
2nd 15 5
3rd 22 6
4th 24 6
5th 36 7
6th 44 7
7th 51 8
8th 58 8
Total 258ms 51ms
We're also tring to optimize the QEMU part [1], but it's still
worth to optimize the KVM to gain more benefits.
[1] https://lists.gnu.org/archive/html/qemu-devel/2021-08/msg04215.html
Signed-off-by: Longpeng(Mike) <longpeng2@huawei.com>
Message-Id: <20210827080003.2689-1-longpeng2@huawei.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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