massive load average spikes

markham breitbach markham_breitbach at
Wed Aug 11 17:39:17 UTC 2010

 Good Day,

I am running into an issue where I am seeing load average on a server suddenly jump from
nominal values around 0.5 to anywhere from 10 up over 70 in under 1 second.  This does not
seem to be related to CPU overload, and LA immediately begins to fall back again to
nominal.  This does not seem to happen with any regular frequency, and can happen several
times an hour or not for hours.

I am running 6.4-RELEASE-p8 with the SMP kernel and interrupt polling enabled.  (I have
also tried without either)

The server is running a mail server in a jail (sendmail, dovecot, etc) with the jail being
a full "build world" and servicing about 2000 users for SMTP, POP3 and IMAP.

The hardware is a Silicon Mechanics (Super Micro) dual 4core Xeon (E5405) with 4GB RAM and
multiple 7200 RPM sata.

I have tried watching top, vmstat, iostat and systat to see if I can correlate something
to these spikes in load average, but nothing really stands out.

Can anyone suggest what may be causing this or how to track that down?

Many Thanks,

Markham Breitbach
SSi Network Operations

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