idprio processes slowing down system

Peter Jeremy peterjeremy at acm.org
Sun Nov 28 07:26:30 UTC 2010


Since scheduler issues have been popular lately, I thought I'd
investigate a ULE issue I've been aware of for a while...

I normally have some boinc (ports/astro/boinc) applications running
and I'd noticed that my nightly builds appear to end much sooner when
there's no boinc work units (this has been common for setiathome).
This morning, I timed 4 "make -j3 KERNCONF=GENERIC buildkernel" of
8-stable with the following results:
boinc running:
1167.839u 287.055s 18:45.69 129.2%        6140+1975k 1+0io 114pf+0w
1166.431u 288.265s 18:00.16 134.6%        6139+1975k 0+0io 106pf+0w
1168.490u 287.599s 17:52.24 135.7%        6137+1975k 0+0io 106pf+0w
1165.747u 287.641s 17:10.38 141.0%        6138+1975k 0+0io 106pf+0w

boinc stopped:
1165.052u 291.492s 15:54.72 152.5%        6125+1972k 0+0io 106pf+0w
1166.101u 290.305s 15:42.54 154.5%        6132+1973k 0+0io 106pf+0w
1165.248u 290.335s 15:35.93 155.5%        6132+1974k 0+0io 106pf+0w
1166.100u 289.749s 15:26.35 157.1%        6137+1974k 0+0io 106pf+0w

Since the the results were all monotonically reducing in wallclock
time, I decided to do a further 4 buildkernels with boinc running:

1168.242u 284.693s 17:33.05 137.9%        6140+1975k 0+0io 106pf+0w
1167.191u 285.332s 17:19.27 139.7%        6140+1976k 0+0io 106pf+0w
1224.813u 291.963s 20:14.90 124.8%        6121+1966k 0+0io 106pf+0w
1213.132u 294.564s 19:48.98 126.8%        6116+1967k 0+0io 106pf+0w

ministat(1) reports there is no statistical difference in the user
or system time:

User time:
x boinc_running
+ boinc_stopped
+----------------------------------------------------------------------+
|         +* x                                                         |
|         +*xx                                            x           x|
||________|A_M___________A_______________________|                     |
+----------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   8      1165.747      1224.813      1168.242     1180.2356      24.12896
+   4      1165.052      1166.101        1166.1     1165.6253    0.55457454
No difference proven at 95.0% confidence

System time:
x boinc_running
+ boinc_stopped
+----------------------------------------------------------------------+
|                                       +                              |
|x   x            x  xx   x         +   +        +  x                 x|
|   |_________________M____A________|___MA_____|__|                    |
+----------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   8       284.693       294.564       287.641       288.389     3.3142183
+   4       289.749       291.492       290.335     290.47025    0.73252412
No difference proven at 95.0% confidence

But there is a significant difference in the wallclock time:
x boinc_running
+ boinc_stopped
+----------------------------------------------------------------------+
|+ + +  +                 x x  x    x x          x              x     x|
||__AM_|                  |___________M____A_______________|           |
+----------------------------------------------------------------------+
    N           Min           Max        Median           Avg        Stddev
x   8       1030.38        1214.9       1080.16     1100.5838     69.364795
+   4        926.35        954.72        942.54       939.885     11.915879
Difference at 95.0% confidence
        -160.699 +/- 79.6798
        -14.6012% +/- 7.23977%
        (Student's t, pooled s = 58.4006)

Since all the boinc processes are running at i31, why are they impacting
a buildkernel that runs with 0 nicety?

System information: AMD Athlon(tm) Dual Core Processor 4850e
(2511.45-MHz K8-class CPU) running FreeBSD/amd64 from just before
8.1-RELEASE with WITNESS and WITNESS_SKIPSPIN, 8GB RAM, src and obj
are both on ZFS.

-- 
Peter Jeremy
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