On 1/23/2026 11:49 AM, Paul E. McKenney wrote: > We could have one CPU flooding and the rest idle, and many other > combinations. And, if I recall correctly, polling can burn extra CPU > and cause extra wakeups even when the system is fully idle. Or has > that changed?
In my experience working on lazy RCU, if you have such a kind of overload on any CPU, then you're usually not saving any power anyway. The system has to be really quiet and idle with a low stream of callbacks for you to save power. Further, when the callback length increases too much, we don't turn on lazy RCU anyway because the idea is that we are overloaded and the system is busy - so we already have such assumptions baked in. I think a similar argument could apply here for dynamically enabling polling mode only when overloaded. I was coming more from the point of view of improving grace period performance when we do have an overload, potentially resolving the overloaded situation faster than usual. We would dynamically trigger polling based on such circumstances. That said, I confess I don't have extensive experience with polling mode beyond testing. I believe we should add more rcutorture test cases for this. I'm considering adding a new config that enables polling for NOCB - this testing is what revealed the potential for grace period performance improvement with NOCB to me. -- Joel Fernandes
