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SubjectRe: [Patch 0/6] delay accounting & taskstats fixes
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On Tue, 2006-07-11 at 00:23, Shailabh Nagar wrote:
> Some results showing the cpumask feature
> works as expected will follow separately.

To illustrate the basic premise behind the cpumask changes
namely, reducing the number of cpus results in fewer overflow
conditions, Chandra ran the following experiment on an
8-way PIII box:

- "mkthreads 1000 1000" (the program which only forks/exits) with
minimum time spent inside the thread function. This is basically an exit
rate that is higher than the 1000/cpu/sec discussed earlier.

- A slightly modified version of the getdelays.c example that is
included in patch 2/6 in this series of postings. Modification was
to print only the number of receives and number of ENOBUFS seen.

The -m parameter specifies the cpumask,
-r parameter is the size of the socket receive buffer
-l results in listening for exit data


The following sets of runs are self-explanatory.
Initial run emulates the earlier behaviour where one listener
receives data for all cpus. As the number of cpus to which it
listens is reduced, the ENOBUFS reduce.

Similarly, increasing the receive buffer size also cuts down
on the ENOBUFS, further helped by reducing number of cpus listened
to. The final data point, not shown here, is when the receive
buffer size is set to some high number like 8K when the ENOBUFS aren't
seen at all.


===================================
Each output shows
stats <number of msgs rcvd> enobufs <num of enobufs seen>
cumulatively

elm3b94:/tmp # ./getdelays -m 0-7 -r 512 -l
cpumask 0-7 maskset 1
receive buf size 512
listen forever
stats 100000, enobufs 2540
stats 200000, enobufs 5701
stats 300000, enobufs 8482
stats 400000, enobufs 11332
stats 500000, enobufs 14256
stats 600000, enobufs 17150
stats 700000, enobufs 19981
stats 800000, enobufs 22971
stats 900000, enobufs 26324
stats 1000000, enobufs 29291
elm3b94:/tmp # ./getdelays -m 0-3 -r 512 -l
cpumask 0-3 maskset 1
receive buf size 512
listen forever
stats 100000, enobufs 831
stats 200000, enobufs 1772
stats 300000, enobufs 2728
stats 400000, enobufs 3820
stats 500000, enobufs 5030
stats 600000, enobufs 6501
stats 700000, enobufs 7885
stats 800000, enobufs 8971
stats 900000, enobufs 10262
stats 1000000, enobufs 11786
elm3b94:/tmp # ./getdelays -m 2-3 -r 512 -l
cpumask 2-3 maskset 1
receive buf size 512
listen forever
stats 100000, enobufs 106
stats 200000, enobufs 206
stats 300000, enobufs 313
stats 400000, enobufs 389
stats 500000, enobufs 477
stats 600000, enobufs 676
stats 700000, enobufs 860
stats 800000, enobufs 1048
stats 900000, enobufs 1189
stats 1000000, enobufs 1303
elm3b94:/tmp # ./getdelays -m 0 -r 512 -l
cpumask 0 maskset 1
receive buf size 512
listen forever
stats 100000, enobufs 100
stats 200000, enobufs 162
stats 300000, enobufs 302
stats 400000, enobufs 399
stats 500000, enobufs 507
stats 600000, enobufs 571
stats 700000, enobufs 666
stats 800000, enobufs 725
stats 900000, enobufs 821
stats 1000000, enobufs 909
================= with recv buf size 2048
elm3b94:/tmp # ./getdelays -m 0-7 -r 2048 -l
cpumask 0-7 maskset 1
receive buf size 2048
listen forever
stats 100000, enobufs 35
stats 200000, enobufs 88
stats 300000, enobufs 123
stats 400000, enobufs 138
stats 500000, enobufs 155
stats 600000, enobufs 191
stats 700000, enobufs 223
stats 800000, enobufs 238
stats 900000, enobufs 280
stats 1000000, enobufs 319

elm3b94:/tmp # ./getdelays -m 4-7 -r 2048 -l
cpumask 4-7 maskset 1
receive buf size 2048
listen forever
stats 100000, enobufs 10
stats 200000, enobufs 17
stats 300000, enobufs 28
stats 400000, enobufs 35
stats 500000, enobufs 49
stats 600000, enobufs 63
stats 700000, enobufs 80
stats 800000, enobufs 94
stats 900000, enobufs 114
stats 1000000, enobufs 138
elm3b94:/tmp # ./getdelays -m 2-3 -r 2048 -l
cpumask 2-3 maskset 1
receive buf size 2048
listen forever
stats 100000, enobufs 5
stats 200000, enobufs 6
stats 300000, enobufs 10
stats 400000, enobufs 14
stats 500000, enobufs 19
stats 600000, enobufs 33
stats 700000, enobufs 38
stats 800000, enobufs 43
stats 900000, enobufs 54
stats 1000000, enobufs 59

elm3b94:/tmp # ./getdelays -m 1 -r 2048 -l
cpumask 1 maskset 1
receive buf size 2048
listen forever
stats 100000, enobufs 3
stats 200000, enobufs 6
stats 300000, enobufs 19
stats 400000, enobufs 25
stats 500000, enobufs 30
stats 600000, enobufs 31
stats 700000, enobufs 33
stats 800000, enobufs 45
stats 900000, enobufs 48
stats 1000000, enobufs 52

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