commit e9e9250b: sync wakeup bustage when waker is an RT task

Mike Galbraith
2010-05-15T11:57:13Z

Hi Peter,

This commit excluded RT tasks from rq->load, was that intentional? The
comment in struct rq states that load reflects *all* tasks, but since
this commit, that's no longer true.

Looking at lmbench lat_udp in a PREEMPT_RT kernel, I noticed that
wake_affine() is failing for sync wakeups when it should not. It's
doing so because the waker in this case is an RT kernel thread
(sirq-net-rx) - we subtract the sync waker's weight, when it was never
added in the first place, resulting in this_load going gaga. End result
is quite high latency numbers due to tasks jabbering cross-cache.

If the exclusion was intentional, I suppose I can do a waker class check
in wake_affine() to fix it.

-Mike