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    SubjectRe: [PATCH v2] IPI performance benchmark
    On Wed, Dec 20, 2017 at 02:44:25PM +0800, Wanpeng Li wrote:
    > Hi Yury,
    > 2017-12-19 16:50 GMT+08:00 Yury Norov <ynorov@caviumnetworks.com>:
    > > This benchmark sends many IPIs in different modes and measures
    > > time for IPI delivery (first column), and total time, ie including
    > > time to acknowledge the receive by sender (second column).
    > >
    > > The scenarios are:
    > > Dry-run: do everything except actually sending IPI. Useful
    > > to estimate system overhead.
    > > Self-IPI: Send IPI to self CPU.
    > > Normal IPI: Send IPI to some other CPU.
    > > Broadcast IPI: Send broadcast IPI to all online CPUs.
    > > Broadcast lock: Send broadcast IPI to all online CPUs and force them
    > > acquire/release spinlock.
    > >
    > > The raw output looks like this:
    > > [ 155.363374] Dry-run: 0, 2999696 ns
    > > [ 155.429162] Self-IPI: 30385328, 65589392 ns
    > > [ 156.060821] Normal IPI: 566914128, 631453008 ns
    > > [ 158.384427] Broadcast IPI: 0, 2323368720 ns
    > > [ 160.831850] Broadcast lock: 0, 2447000544 ns
    > >
    > > For virtualized guests, sending and reveiving IPIs causes guest exit.
    > > I used this test to measure performance impact on KVM subsystem of
    > > Christoffer Dall's series "Optimize KVM/ARM for VHE systems" [1].
    > >
    > > Test machine is ThunderX2, 112 online CPUs. Below the results normalized
    > > to host dry-run time, broadcast lock results omitted. Smaller - better.
    >
    > Could you test on a x86 box? I see a lot of calltraces on my haswell
    > client host, there is no calltrace in the guest, however, I can still
    > observe "Invalid parameters" warning when insmod this module. In
    > addition, the x86 box fails to boot when ipi_benchmark is buildin.

    EINVAL is returned intentionally to let user run test again without
    annoying rmmod.

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