Re: Strange load spikes on 2.4.19 kernel

Rob Mueller
2002-10-13T06:30:01Z

We've just discovered that this is actually happening on another one of our
machines as well. This machine uses 2.4.18 kernel, ext3 and has 2 SCSI
drives and 2 IDE drives which hold the main user mailbox data. Also it's a
P3 with a completely different motherboard rather than an Athlon, so it
doesn't seem to be hardware related in that respect.

> well, it's conceivable that if something is blocking a bunch
> of procs, it would also block your shell and ps, so not show up.
> "vmstat 1" might work better, though it's munging plenty of
> /proc files so is hardly immune to that.

But the ps/shell would only use CPU time, and there's plenty of that
available. Unless it was something everything would block on... what could
that be? A spin lock or something? Some interrupt routine? Would that even
result in other processes being counted as blocked process?

Also Let me do a calculation, though I have no idea if this is right or
not...
a) the first item in the uptime output is 'system load average for the last
1 minute'
b) it seems to only update/recalculate every 5 seconds
c) it jumps from < 1 to 20 in 1 interval (eg 5 seconds)

This means that for it to jump from < 1 to 20 in 5 seconds, there must be on
average about 60/5 * 20 = 240 processes blocked over those 5 seconds waiting
for run time of some sort for the load to jump 20 points. Is that right?

> but it's worth asking: do you notice a hiccup other than by looking
> at the loadav? that is, suppose the loadav is simply miscalculated...

Well yes, there definitely does seem to be a performance hit on the whole
system when the load jumps, everything feels significantly more 'sluggish'
during the spikes is the best I can describe it right now...

Rob