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DateFri, 18 Sep 1998 04:41:56 -0400 (EDT)
FromIon Badulescu <>
SubjectPainfully slow exec() on 2.0.35/36?
Hello,

I'm having a problem on a news server and I'm not sure what to blame,
since quite a few things have change in its configuration. I *think* it's
not a problem with the latest 2.0.36pre snapshots, as I tried 2.0.35 and
didn't make any difference. It's most probably inn-2.1's fault, but I
think the issue is worth investigating a little further.

This is what happens: the server is getting a pretty fat feed, so its load
average hovers usually around 2-3. Even so, it is pretty snappy. However,
a news *reader* connection is established only after a very annoying
delay, during which innd fork()'s and then exec()'s nnrpd.

strace output shows that it's the exec() syscall itself that's taking an
unusual amount of time -- between 10 and 50 seconds! While this is
happening, ps -axl shows the process doing the exec() as

100040     6 15998 30053   7   4      0     0 wait_on_buf DWN   ? 0:00 \_/usr/local/news/bin/innd -p7 

and, what's more weird, vmstat 1 shows "lots" of blocks being written to
the disk, a lot more than usual:

 procs                  memory    swap        io    system         cpu
 r b w  swpd  free  buff cache  si  so   bi   bo   in   cs  us  sy  id
 0 2 4  5432  2164 43368 50568   0   0  348 3052  849  359  11  37  51
 0 3 4  5432  2216 43472 50596   0   0  246 2000  564  279   4  24  72
 0 2 4  5432  2076 43476 50640   0   0  388 3000  886  315   5  31  64
 1 1 4  5432  2016 43476 50672   0   0  281 2500  655  293   1  23  76
 1 2 4  5432  1868 43476 50808   0   0  450 2500  827  738   8  28  63
 2 1 4  5432  1128 43224 50500   8   0  324 3020  723  273   9  37  54

whereas the usual output is more like:

 procs                  memory    swap        io    system         cpu
 r b w  swpd  free  buff cache  si  so   bi   bo   in   cs  us  sy  id
 1 1 0  5432  2188 47992 52356   0   0  303    0  766  239   9   8  84
 0 2 0  5432  2128 47948 52352   0   0  192 1260 1012  590   4  16  80
 1 0 0  5432  1592 47864 52344   0   0   78  289 1289  380  11  15  75
 0 1 0  5432  1704 47776 52480   0   0  395    0  671  268   5   9  87
 1 0 0  5432  1752 47716 52480   0   0  329    0  553  341   7   5  88

The machine has 128MB of RAM and is barely using any swap at all, around
5MB. The system also has the news stuff spread across 7 or so disk
spindles, so it's not an issue of slowly reading nnrpd from the disk.

I'm really puzzled. Anybody has a good explanation for this?

Thanks,
Ion

-- 
  It is better to keep your mouth shut and be thought a fool,
            than to open it and remove all doubt.


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