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    SubjectRe: [RFC][Patch] Retry based aio read for filesystems
    Suparna Bhattacharya wrote:

    > For the last few days I've been playing with prototyping
    > a particular flavour of a retry based implementation for
    > filesystem aio read.

    Hi Suparna,

    I ran an aio-enabled version of fsx on your patches and no errors were
    reported. I plan on using gcov to determine the test coverage I
    obtained.

    I also did a quick performance test using wall time to compare sync and
    async read operations with your patches applied. For the sync case I
    ran
    10 processes in parallel, each reading 1GB in 1MB chunks from a
    per-process
    dedicated device. I compared that to a single aio process iteratively
    calling
    io_submit/io_getevents for up to 10 iocbs/events where each iocb
    specified a
    1MB read to its dedicated device until 1GB was read. Whew!

    The result was that wall time for the sync and async testcases were
    consistently identical, i.e., 1m30s:

    # sync_test
    start time: Wed Mar 5 14:02:05 PST 2003
    end time: Wed Mar 5 14:03:35 PST 2003

    # aio_test
    start time: Wed Mar 5 13:52:04 PST 2003
    end time: Wed Mar 5 13:53:34 PST 2003

    syncio vmstat:
    procs memory swap io
    system cpu
    r b w swpd free buff cache si so bi bo in cs us
    sy id
    4 6 2 3324 3888 11356 3668848 0 0 151296 0 2216 2395 0
    100 0
    4 6 1 3324 3888 11368 3668820 0 0 151744 5 2216 2368 0
    100 0
    1 9 1 3324 3952 11368 3668860 0 0 151209 1 2213 2356 0
    100 0
    5 5 1 3324 3940 11344 3668864 0 2 148948 3 2215 2387 0
    100 0
    1 9 1 3348 3936 11264 3668968 0 6 150767 7 2209 2345 0
    100 0
    6 4 1 3480 3920 11192 3669364 0 33 151456 33 2218 2340 0
    100 0
    4 6 2 3568 3896 11316 3669352 0 21 151887 21 2218 2385 0
    100 0
    7 3 1 3704 3820 11364 3669428 31 34 148687 35 2222 2344
    1 99 0

    aio vmstat:
    procs memory swap io
    system cpu
    r b w swpd free buff cache si so bi bo in cs us
    sy id
    2 0 1 4016 4040 11192 3669644 0 17 133152 25 2073 502
    0 40 60
    1 0 1 4016 4104 11196 3669716 0 0 132288 1 2073 537
    0 40 60
    2 0 2 4016 4104 11196 3669764 0 0 132416 0 2067 511
    0 40 60
    1 0 1 4016 4104 11200 3669788 0 0 133088 1 2075 523
    0 41 59
    1 0 1 4016 5576 11200 3668240 0 0 132384 0 2066 526
    0 40 60
    1 0 1 4036 4092 11200 3669756 0 5 135116 5 2094 492
    0 46 54
    1 0 1 4180 4016 11192 3669944 0 36 135968 40 2111 499
    0 46 54
    2 0 2 4180 4060 11176 3669832 0 0 137152 0 2119 463
    1 46 53
    1 0 1 4180 7060 11180 3666980 0 0 136384 2 2107 498
    0 44 56


    -Janet

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