 | | | Meaning of 'load ' on Linux | Meaning of 'load ' on Linux 2005-06-16 - By Tom Sightler
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On Thu, 2005-06-16 at 11:42 +0200, Mimmus wrote:
> He said me that "load" on Linux (i.e. output of 'uptime' or 'top') has a
> different meaning than in other Unixes. Under HP-UX, I was comfortable with
> values under 2-2.5; he said that under Linux 10-12 is normal and that he saw
> working servers with load even of 1000 (!) using Oracle 'custom' kernels.
Well, I'm pretty confident that load under HP-UX and under Linux were at
least originally the same. Basically, load the average number of
processes in the runqueue during the given intervals of time. I'm
pretty sure both HP-UX and Linux use this same basic definition.
For example, our central database server currently has the following
load:
load average: 2.35, 2.29, 2.25
That means that for the last 1, 5, and 15 minutes that typically 2.25
processes have been runnable (or possible 'D' state) at any given time.
Since this is an 8-cpu system that's certainly no real concern as that's
roughly 25% of the total capacity. You should be able to roughly bear
this out with sar. With a load average of 2.25 I would expect to see
approximate 28% of CPU time used and sure enough, here the last two
lines of my sar output from my Oracle database server:
CPU %user %nice %system %iowait %idle
10:10:00 AM all 35.33 0.00 3.05 2.55 59.07
10:20:00 AM all 21.33 0.00 3.59 2.72 72.36
Reasonably close to my prediction based from load average, but not
exactly the same because they don't quite cover the same time periods.
During very busy periods I see loads as high as 20-25 for short periods
of time (< a few minutes).
A load of 1000 sounds crazy, but may not be based on how it is
generated. My guess is it was generated during some benchmark rather
than a production, but I suppose a highly concurrent environment with
1000's of concurrent users might generate that load. I've run web
benchmarks that pushed the load average to 100+ during the benchmark on
a 2-way system even though response to the clients stayed acceptable.
Later,
Tom
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