On Wed, Dec 13, 2017 at 03:23:21PM +0530, Viresh Kumar wrote: > Currently the schedutil governor overwrites the sg_cpu->flags field on > every call to the utilization handler. It was pretty good as the initial > implementation of utilization handlers, there are several drawbacks > though. > > The biggest drawback is that the sg_cpu->flags field doesn't always > represent the correct type of tasks that are enqueued on a CPU's rq. For > example, if a fair task is enqueued while a RT or DL task is running, we > will overwrite the flags with value 0 and that may take the CPU to lower > OPPs unintentionally. There can be other corner cases as well which we > aren't aware of currently. > > This patch changes the current implementation to keep track of all the > task types that are currently enqueued to the CPUs rq. A new flag: CLEAR > is introduced and is set by the scheduling classes when their last task > is dequeued. When the CLEAR flag bit is set, the schedutil governor resets > all the other flag bits that are present in the flags parameter. For > now, the util update handlers return immediately if they were called to > clear the flag.
Yeah, not happy about this either; we had code that did the right thing without this extra tracking I think. Also, we can look at the rq state if we want to, we don't need to duplicate that state.
