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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.30-9
    Ingo Molnar wrote:
    > i have released the -V0.7.30-9 Real-Time Preemption patch, which can be
    > downloaded from the usual place:
    >

    A couple of observations that I would like to share:

    1) With all of the tracing compiled in, there is a measurable amount of
    additional latency, even when the tracing is disabled via the proc
    interfaces. So if you want to measure best-case (or worst-case)
    latencies turn off the tracing facilities to do so. For example, using a
    blocking read, the worst case latency from interrupt to read: wo/tracing
    ~68 usec, w/tracing ~110 usec. I am attaching two histograms generated
    by the rtc histogram by running a slightly modified version of realfeel.

    2) Also there is a big difference in latencies between blocking reads
    and using signals to notify the process that data is available. I am
    also attaching a histogram generated by the rtc histogram by running
    amlat. Part of the numbers in the > 10 msec bucket are into the hundreds
    of msecs.

    All of these numbers were generated using a comparable load from
    stress-kernel.

    kr




    No tracing using read:
    rtc latency histogram of {realfeel/5162, 671921 samples}:
    3 221135
    4 32396
    5 38047
    6 62650
    7 99079
    8 62347
    9 47702
    10 37572
    11 27323
    12 16734
    13 9889
    14 6081
    15 3607
    16 2214
    17 1440
    18 784
    19 494
    20 355
    21 269
    22 215
    23 186
    24 163
    25 124
    26 123
    27 93
    28 85
    29 85
    30 90
    31 80
    32 61
    33 72
    34 47
    35 53
    36 49
    37 39
    38 29
    39 26
    40 22
    41 15
    42 19
    43 18
    44 23
    45 15
    46 12
    47 4
    48 10
    49 12
    50 4
    51 4
    52 4
    53 3
    54 2
    55 4
    56 3
    57 2
    59 1
    60 1
    61 1
    62 1
    67 1
    68 2
    Tracing on using read:
    Nov 22 19:37:39 porky kernel: rtc latency histogram of {realfeel/6592, 487037 samples}:
    Nov 22 19:37:39 porky kernel: 13 10
    Nov 22 19:37:39 porky kernel: 14 88142
    Nov 22 19:37:39 porky kernel: 15 113256
    Nov 22 19:37:39 porky kernel: 16 77884
    Nov 22 19:37:39 porky kernel: 17 60492
    Nov 22 19:37:39 porky kernel: 18 41451
    Nov 22 19:37:39 porky kernel: 19 23587
    Nov 22 19:37:39 porky kernel: 20 15409
    Nov 22 19:37:39 porky kernel: 21 11975
    Nov 22 19:37:39 porky kernel: 22 14672
    Nov 22 19:37:39 porky kernel: 23 11843
    Nov 22 19:37:39 porky kernel: 24 8318
    Nov 22 19:37:39 porky kernel: 25 5595
    Nov 22 19:37:39 porky kernel: 26 3546
    Nov 22 19:37:39 porky kernel: 27 2057
    Nov 22 19:37:39 porky kernel: 28 1192
    Nov 22 19:37:39 porky kernel: 29 819
    Nov 22 19:37:39 porky kernel: 30 682
    Nov 22 19:37:39 porky kernel: 31 665
    Nov 22 19:37:39 porky kernel: 32 662
    Nov 22 19:37:39 porky kernel: 33 540
    Nov 22 19:37:39 porky kernel: 34 494
    Nov 22 19:37:39 porky kernel: 35 433
    Nov 22 19:37:39 porky kernel: 36 290
    Nov 22 19:37:39 porky kernel: 37 227
    Nov 22 19:37:39 porky kernel: 38 189
    Nov 22 19:37:39 porky kernel: 39 129
    Nov 22 19:37:39 porky kernel: 40 110
    Nov 22 19:37:39 porky kernel: 41 78
    Nov 22 19:37:39 porky kernel: 42 85
    Nov 22 19:37:39 porky kernel: 43 102
    Nov 22 19:37:39 porky kernel: 44 314
    Nov 22 19:37:39 porky kernel: 45 189
    Nov 22 19:37:39 porky kernel: 46 137
    Nov 22 19:37:39 porky kernel: 47 105
    Nov 22 19:37:39 porky kernel: 48 147
    Nov 22 19:37:39 porky kernel: 49 101
    Nov 22 19:37:39 porky kernel: 50 99
    Nov 22 19:37:39 porky kernel: 51 93
    Nov 22 19:37:39 porky kernel: 52 61
    Nov 22 19:37:39 porky kernel: 53 57
    Nov 22 19:37:39 porky kernel: 54 44
    Nov 22 19:37:39 porky kernel: 55 50
    Nov 22 19:37:39 porky kernel: 56 49
    Nov 22 19:37:39 porky kernel: 57 50
    Nov 22 19:37:39 porky kernel: 58 48
    Nov 22 19:37:39 porky kernel: 59 49
    Nov 22 19:37:39 porky kernel: 60 41
    Nov 22 19:37:39 porky kernel: 61 31
    Nov 22 19:37:39 porky kernel: 62 23
    Nov 22 19:37:39 porky kernel: 63 19
    Nov 22 19:37:39 porky kernel: 64 23
    Nov 22 19:37:39 porky kernel: 65 27
    Nov 22 19:37:39 porky kernel: 66 18
    Nov 22 19:37:39 porky kernel: 67 17
    Nov 22 19:37:39 porky kernel: 68 15
    Nov 22 19:37:39 porky kernel: 69 16
    Nov 22 19:37:39 porky kernel: 70 17
    Nov 22 19:37:39 porky kernel: 71 11
    Nov 22 19:37:39 porky kernel: 72 11
    Nov 22 19:37:39 porky kernel: 73 19
    Nov 22 19:37:40 porky kernel: 74 15
    Nov 22 19:37:40 porky kernel: 75 24
    Nov 22 19:37:40 porky kernel: 76 26
    Nov 22 19:37:40 porky kernel: 77 14
    Nov 22 19:37:40 porky kernel: 78 15
    Nov 22 19:37:40 porky kernel: 79 17
    Nov 22 19:37:40 porky kernel: 80 19
    Nov 22 19:37:40 porky kernel: 81 12
    Nov 22 19:37:40 porky kernel: 82 4
    Nov 22 19:37:40 porky kernel: 83 7
    Nov 22 19:37:40 porky kernel: 84 9
    Nov 22 19:37:40 porky kernel: 85 8
    Nov 22 19:37:40 porky kernel: 86 11
    Nov 22 19:37:40 porky kernel: 87 8
    Nov 22 19:37:40 porky kernel: 88 4
    Nov 22 19:37:40 porky kernel: 89 3
    Nov 22 19:37:40 porky kernel: 90 1
    Nov 22 19:37:40 porky kernel: 91 5
    Nov 22 19:37:40 porky kernel: 92 5
    Nov 22 19:37:40 porky kernel: 94 3
    Nov 22 19:37:40 porky kernel: 95 1
    Nov 22 19:37:40 porky kernel: 96 2
    Nov 22 19:37:40 porky kernel: 97 2
    Nov 22 19:37:40 porky kernel: 98 2
    Nov 22 19:37:40 porky kernel: 99 1
    Nov 22 19:37:40 porky kernel: 101 1
    Nov 22 19:37:40 porky kernel: 107 2
    Nov 22 19:37:40 porky kernel: 110 1
    No tracing using signals:
    rtc latency histogram of {amlat/7215, 535020 samples}:
    4 1
    9 18916
    10 125448
    11 29422
    12 41496
    13 22222
    14 15344
    15 12256
    16 10935
    17 11157
    18 11192
    19 11456
    20 12994
    21 13832
    22 14704
    23 14330
    24 12625
    25 11837
    26 11839
    27 11206
    28 10307
    29 10057
    30 10183
    31 13115
    32 11438
    33 11897
    34 11559
    35 7817
    36 5823
    37 4660
    38 3944
    39 3106
    40 2763
    41 2424
    42 1961
    43 1729
    44 1348
    45 1154
    46 984
    47 801
    48 682
    49 537
    50 467
    51 345
    52 288
    53 214
    54 182
    55 162
    56 131
    57 117
    58 135
    59 118
    60 111
    61 120
    62 118
    63 89
    64 103
    65 95
    66 92
    67 85
    68 62
    69 45
    70 61
    71 39
    72 29
    73 40
    74 28
    75 25
    76 25
    77 18
    78 18
    79 11
    80 13
    81 9
    82 13
    83 10
    84 11
    85 5
    86 2
    87 4
    88 2
    89 3
    90 2
    91 5
    92 2
    93 1
    94 2
    95 4
    96 3
    97 2
    98 1
    99 3
    103 1
    104 1
    108 2
    118 1
    7860 1
    9999 43
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