Re: [squid-users] Uneven load distribution between SMP Workers

On 07/30/2013 06:44 AM, Tim Murray wrote:

> I'm running Squid 3.3.5 on 3 multicore systems here, using SMP and 6
> workers per server dedicated to their own core. Each one running OS
> RHEL6 U4 with 2.6.32 kernel.
>
> I'm noticing as time goes on, some workers seem to be favoured and
> doing the majority of the work. I've read the article regarding SMP
> Scaling here:
>
> http://wiki.squid-cache.org/Features/SmpScale
>
> However I'm find our workers CPU time is differing quite substantially;

As discussed on the above wiki page, this is expected. We see it all the
time on many boxes, especially if Squid is not very loaded. IIRC, the
patch working around that problem has not been submitted for the
official review yet -- no free cycles to finish its polishing at the moment.

> I can also see the connections differ massively between the workers:

Same thing.

> I'm a little concerned that the more people I migrate to this solution
> the more the first 1 or 2 workers will become saturated. Do the
> workers happen to have some form of source or destination persistance
> for (SSL?) connections or something that might be causing this to
> occur?

The wiki page provides the best explanation of the phenomena I know
about. In short, some kernels (including their TCP stacks) are not very
good at balancing this kind of server load.

> And is there anything I can do to improve the distribution between
> workers?

I am not aware of any specific fix, except for the workaround patch
mentioned on the wiki.

Alex.
Received on Tue Jul 30 2013 - 17:44:35 MDT