Hi John,
...
/** Wa_14019159160: disable the automatic CCS load balancingI'm still a bit concerned that this doesn't really match what this specific workaround is asking us to do. There seems to be an agreement on various internal email threads that we need to disable load balancing, but there's no single specific workaround that officially documents that decision.
This specific workaround asks us to do a bunch of different things, and the third item it asks for is to disable load balancing in very specific cases (i.e., while the RCS is active at the same time as one or more CCS engines). Taking this workaround in isolation, it would be valid to keep load balancing active if you were just using the CCS engines and leaving the RCS idle, or if balancing was turned on/off by the GuC scheduler according to engine use at the moment, as the documented workaround seems to assume will be the case.
So in general I think we do need to disable load balancing based on other offline discussion, but blaming that entire change on Wa_14019159160 seems a bit questionable since it's not really what this specific workaround is asking us to do and someone may come back and try to "correct" the implementation of this workaround in the future without realizing there are other factors too. It would be great if we could get hardware teams to properly document this expectation somewhere (either in a separate dedicated workaround, or in the MMIO tuning guide) so that we'll have a more direct and authoritative source for such a large behavioral change.
On one had I think you are right, on the other hand I think this workaround has not properly developed in what we have been describing later.
I think it is not so much that the w/a is 'not properly developed'. It's more that this w/a plus others when taken in combination plus knowledge of future directions has led to an architectural decision that is beyond the scope of the w/a.
As such, I think Matt is definitely correct. Tagging a code change with a w/a number when that change does something very different to what is described in the w/a is wrong and a maintenance issue waiting to happen.
At the very least, you should just put in a comment explaining the situation. E.g.:
/*
- Wa_14019159160: This w/a plus others cause significant issues with the use of
- load balancing. Hence an architectural level decision was taking to simply
- disable automatic CCS load balancing completely.
*/
Good suggestion! I will anyway check tomorrow with Joonas if it's worth the effort to set up a new "software" workaround.
Thanks, Andi