[distcc] DISTCC_POTENTIAL_HOSTS, localhost, and slots

[Fergus Henderson]

On Wed, May 14, 2014 at 6:16 AM, Dave Abrahams <dave at boostpro.com> wrote:

> DISTCC_POTENTIAL_HOSTS seems like a great idea; as I scale up the build
> farm I’d like to be able to deal with unavailability, but I’m having
> trouble getting it to work right.
>
> First, after much fooling around I surmise two undocumented facts(?)
>
> 1. it adds ,lzo,cpp to all the hosts implicitly
>

Yes, that's done in ExportDISTCC_HOSTS function in the pump script (source
file pump.in).


> 2. it only accepts bare host names, not the usual
> @?hostname/<slots>(,<extension>)* syntax
>
Is that correct?
>

Pretty much, yes.  It just passes the variable's value to lsdistcc, and
lsdistcc accepts either bare host names, or a printf format string
containing %d, e.g. "mydistcc%d" or "distcc%d.my.own.org.com", not *host
specifications* as described the distcc man page.

If so, it would be good if these things were documented explicitly
> somewhere.
>

Agreed.  I would be happy to accept a patch to add such documentation.

Another possibility would be to change lsdistcc to handle host
specifications.


> Also, if I want localhost to be one of the hosts, it looks like I need to
> run distccd there.  That doesn’t seem like the most efficient thing to do,
> since normal local compilation will presumably have fewer layers to work
> through.  Am I mistaken?
>

Well, you only need to run distccd for lsdistcc's initial query (lsdistcc
doesn't have any special casing for localhost).
But any actual compilations done will not go via the distccd on localhost;
distcc itself does have special casing for localhost.

I'd be happy to accept a patch to src/lsdistcc.c to make it special-case
"localhost".


>  Lastly, I’ve only been able to get it to run the default 6 (?) slots per
> host using DISTCC_POTENTIAL_HOSTS.  My .distcc/hosts file looks like this,
> and has been working pretty well:
>
> --randomize
> localhost/10
> bruford/10,lzo,cpp
> fripp/10,lzo,cpp
>
>
> Is there any way to get an effect like that using DISTCC_POTENTIAL_HOSTS,
> i.e. 10 slots per host, no local distccd?
>

Not currently.  I imagine that it would require only very minor changes to
the ExportDISTCC_HOSTS function in the pump script (source file pump.in),
though.

Cheers,
   Fergus.

-- 
Fergus Henderson <fergus at google.com>

"Defend the user, exclude no one, and create magic." -- Eric Schmidt.
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