On Wed, Feb 26, 2014 at 7:28 AM, Peter Zijlstra <[email protected]> wrote: > On Tue, Feb 18, 2014 at 05:56:51PM -0600, George McCollister wrote: >> dequeue_entity() is called when p->on_rq and sets se->on_rq = 0 >> which appears to guarentee that the !se->on_rq condition is met. >> If the task has done set_current_state(TASK_INTERRUPTIBLE) without >> schedule() the second condition will be met and vruntime will be >> incorrectly adjusted twice. >> >> In certain cases this can result in the task's vruntime never increasing >> past the vruntime of other tasks on the CFS' run queue, starving them of >> CPU time. >> >> This patch changes switched_from_fair() to use !p->on_rq instead of >> !se->on_rq. >> >> I'm able to cause a task with a priority of 120 to starve all other >> tasks with the same priority on an ARM platform running 3.2.51-rt72 >> PREEMPT RT by writing one character at time to a serial tty (16550 UART) >> in a tight loop. I'm also able to verify making this change corrects the >> problem on that platform and kernel version. >> >> I haven't and not sure I will have an opportunity to get a newer kernel >> version running on the platform mentioned above and have yet to >> reproduce the problem on another platform. > > Yes, I think you're quite right. Another way to look at this is that > p->on_rq is the one matching p->state. Yes, correct
> > Can I have (or add) your Signed-off-by for this patch? Go ahead and add my sign off. I didn't want to add it before discussing the issue with someone. Thanks, George McCollister -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
