[Skiboot] [PATCH] Rate limit OPAL_MSG_OCC to only one outstanding message to host

[Patrick Williams]

On Fri, Sep 25, 2015 at 04:40:00PM +1000, Stewart Smith wrote:
> Patrick Williams <patrick at stwcx.xyz> writes:
> > On Fri, Sep 25, 2015 at 10:59:08AM +1000, Stewart Smith wrote:
> >> +{
> >> +	lock(&occ_lock);
> >> +	occ_opal_msg_outstanding = false;
> >> +	unlock(&occ_lock);
> >> +}
> >
> > ...
> >
> >> +				if (!rc) {
> >>  					chip->throttle = occ_data->throttle;
> >> +					occ_opal_msg_outstanding = true;
> >> +					break;
> >
> > Are you sure you don't want these to be ++ / -- ?  With this current
> > implementation you can still run out of memory if a two or more socket
> > system is throwing excessive throttles from both OCCs.
> 
> It's run from a poller, so we only start iterating through the memory
> regions every so often (maybe even only once/second). If we had an
> interrupet (like we'd like) then it'd be a bit more of an issue, but with
> this patch, we still wouldn't have more than one outstanding message to
> linux as we won't poll for a change until after linux has acked the
> previous one.
> 

Line 348 has a 'for_each_chip', so you send a throttled message per
socket in the worst case.  You clear the boolean when you get one
response.  Can't this end up in a 2:1 ratio of sent:recv messages under
load?

-- 
Patrick Williams
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