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    SubjectRe: [PATCH 0/2] arm64: cpuidle: make arm_cpuidle_suspend() more efficient
    Hi Will,

    On Thu, 24 Mar 2016 11:15:07 +0000 Will Deacon wrote:

    > On Thu, Mar 24, 2016 at 01:08:48PM +0800, Jisheng Zhang wrote:
    > > This series is to improve the arm_cpuidle_suspend() a bit by removing/moving
    > > out checks from this hot path.
    > >
    > > Jisheng Zhang (2):
    > > arm64: cpuidle: remove cpu_ops check from arm_cpuidle_suspend()
    > > arm64: cpuidle: make arm_cpuidle_suspend() a bit more efficient
    > >
    > > arch/arm64/kernel/cpuidle.c | 9 ++-------
    > > 1 file changed, 2 insertions(+), 7 deletions(-)
    >
    > These look fine to me, but do you have any rough numbers showing what
    > sort of improvement we get from this change?

    Good question. Here it is:

    I measured the 4096 * time from arm_cpuidle_suspend entry point to the
    cpu_psci_cpu_suspend entry point. HW platform is Marvell BG4CT STB board.

    1. only one shell, no other process, hot-unplug secondary cpus, execute the
    following cmd

    while true
    do
    sleep 0.2
    done

    before the patch: 1581220ns

    after the patch: 1579630ns

    reduced by 0.1%

    2. only one shell, no other process, hot-unplug secondary cpus, execute the
    following cmd

    while true
    do
    md5sum /tmp/testfile
    sleep 0.2
    done

    NOTE the testfile size should be larger than L1+L2 cache size

    before the patch: 1961960ns
    after the patch: 1912500ns

    reduced by 2.5%

    So the more complex the system load, the bigger the improvement.

    Thanks,
    Jisheng

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