[RndTbl] load throttling

[Trevor Cordes]

On 2012-01-12 Gilbert E. Detillieux wrote:
> 
> My guess is that your overall processing is disk-bound.  Load average 
> includes not only processes in in the run queue, but those waiting
> for disk I/O (normally, fairly short waits).  The MUUG server sees
> similar loads when a lot of people are hammering at the mirror file
> system (over http, ftp and/or rsync), with relatively low CPU
> percentages.

Could be.  For each mini-job there's a select on a big db, some little
indexed selects and a few tiny db writes.

> Yeah, I think you'll have to experiment, since it depends on how much
> of your load is disk vs CPU.  I would certainly make sure to set the
> target threshold higher than 2, and probably lower than 10.  Maybe
> start with 4, and if your CPU usage is still low, bring it up toward
> 8.

Ya, I think a 3 or 4 load threshold setting might work better.  I'll
play around a bit with it.

On 2012-01-12 John Lange wrote:
> Perhaps setting a "nice" value on the processes might be a easier
> solution?

My long jobs are [io]niced fully.  But, they are heavily mysql
dependent and I can't [io]nice mysqld.  So I can't fully rely on nice
here.  And I find that in practice, even maximum [io]nice doesn't nice
things as much as you'd want.  Nice'd ps's still can grab a huge chunk
of resources.  At least ionice gives you some cool "never run unless
idle" options, though I don't usually use them :-)

On 2012-01-12 Sean Walberg wrote:
> see high load average and low CPU it means you've got high I/O.
> Watching "vmstat 2" usually confirms this with blocked processes on
> the left.

At loadavg 2, vmstat 2 shows about 80% 0 b's, 15% 1 b's and 5% 2 b's.