Re: [PATCH v2 10/10] sched/eevdf: Move to a single runqueue

[Peter Zijlstra]

On Tue, May 26, 2026 at 04:24:32PM +0530, K Prateek Nayak wrote:
> Hello Peter,
> 
> On 5/26/2026 3:22 PM, Peter Zijlstra wrote:
> > On Tue, May 26, 2026 at 02:45:45PM +0530, K Prateek Nayak wrote:
> > 
> >> The suggested diff above solves the crash in my case but your
> >> mileage may vary. Peter can comment if this is the right thing
> >> to do or not :-)
> > 
> > Is this a different issue than the one you raised before?
> 
> Yes, this is different. Essentially, this is what is happening:
> 
>   throttle_cfs_rq_work()
>     task_rq_lock()
> 
>     dequeue_task_fair(current)    /* Task is dequeued on cfs side */
>       __dequeue_task(current)
>         dequeue_hierarchy(current);
>           current->se.on_rq = 0;
>           /* update_load_sub() */
>     resched_curr();               /* Initiates a resched */
> 
>     task_rq_unlock()
>       local_irq_enable();
> 
>   =====> sched_tick()
>           task_tick_fair()
>              __calc_prop_weight()
>                /*
>                 * Oops: update_load_sub() above has
>                 * 0ed the weight of cfs_rq.
>                 */
>   <====
> 
>   preempt_schedule_irq()
>     next = ...
>     put_prev_set_next_task() /* The runtime context is switched here */
> 

Ah, right. OK, I'll go have a poke once I get these proxy patches I've
been spending too much time on posted.

I think I've found a 'problem' with that PROXY_WAKING ==> '->is_blocked
&& !->blocked_on' scheme :-(

> > We talked about throtte, and you were going to make a proper patch of that cleanup
> > iirc.
> 
> I had rebased your suggestion on tip and fixed a couple of splats but
> once it was functional, I noticed hackbench taking twice as long to
> complete compared to tip and I was chasing that before I fell sick.
> 
> Let me go dig deeper to see where exactly it is all going sideways.

Sure, no worries. This happens; computers just never want to just DTRT
already. I lost a day and then some trying to figure out why my
seemingly 'trivial' proxy changes ended up trying to run a dead task
last week...