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    SubjectRe: [RFC] Android Logger vs. Shared Memory FIGHT!
    On 03/29/2012 10:09 AM, Daniel Walker wrote:
    > John Stultz commented on how gettimeofday() is more accurate that what
    > is needed. Logger actually uses a less accurate, and faster, method of timing.
    > The time isn't exactly apples to apples, my shared memory example is actually
    > using a slower clock compared to logger.

    OK - that's interesting.
    >
    >>
    >> Tests were 60 seconds. I presume there were multiple runs and these are
    >> averages. Can you provide the number of runs and the standard deviation for
    >> each set?
    >
    >
    > Test cases were 600 seconds (10 minutes) .. There were three runs.
    > Here's the raw data, all in bytes per second:
    >
    > X86:
    > Logger TSC = 70072480.0, 83911562.7, 78610971.8
    > Shared Memory TSC = 460262336.0, 454204684.1, 457050682.2
    >
    > Logger ACPI_PM = 75523320.0, 81615111.9, 81588600.2
    > Shared Memory ACPI_PM = 29688532.0, 28211029.2, 28225661.6
    >
    >
    > ARM:
    > Logger = 6985508.0, 5827587.3, 7034293.7
    > Shared Memory = 12371886.7, 18362639.9, 15274489.3


    > You can feel free to compute the standard deviation if you wish.

    Here are the std deviations:

    x86-logger-tsc: 7.4%
    x86-shmem-tsc: 0.5%
    x86-logger-ACPI_PM: 3.6%
    x86-shmem-ACPI_PM: 2.4%
    ARM-logger: 8.4%
    ARM-shmem: 15.9%

    Performance ratios:
    x86-shmem-tsc/x86-logger-tsc -> 5.9
    x86-shmem-ACPI_PM/x86-logger-ACPI_PM -> 0.36
    ARM-shem/ARM-logger -> 2.3

    It would be nice to understand why the ARM numbers are
    not more consistent. I'll try to take a look at this next week.

    Thanks for the data.

    I recently started work on my own performance test suite
    for logger. I'm taking the approach of simulating log
    insertions based on log timings from a sampled device, and
    measuring cost per message. I'm not sure when I'll finish
    it, but I'll post results when I have them.
    -- Tim

    =============================
    Tim Bird
    Architecture Group Chair, CE Workgroup of the Linux Foundation
    Senior Staff Engineer, Sony Network Entertainment
    =============================



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