[RFT] IRQ sharing for assigned devices - method selection

[Jan Kiszka <jan.kiszka@web.de>]

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Hi,

to finally select the approach for adding overdue IRQ sharing support
for PCI pass-through, I hacked up two versions based on Thomas' patches
and his suggestion to use a timeout-based mode transition:

    git://git.kiszka.org/linux-kvm.git queues/dev-assign.notify
    git://git.kiszka.org/linux-kvm.git queues/dev-assign.timeout

    git://git.kiszka.org/qemu-kvm.git queues/dev-assign

Both approaches work, but I'm either lacking a sufficiently stressing
test environment to tickle out a relevant delta, even between masking at
irqchip vs. PCI config space level - or there is none... Yes, there are
differences at micro level but they do not manifest in measurable (ie.
above the noise level) load increase or throughput/latency decrease in
my limited tests here. I that actually turns out to be true, I would
happily bury all this dynamic mode switching again.

So, if you have a good high-bandwidth test case at hand, I would
appreciate if you could give this a try and report your findings. Does
switching from exclusive to shared IRQ mode decrease the throughput or
increase the host load? Is there a difference to current kvm?

Thanks in advance,
Jan


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