RE: [PATCH 0/4] sched: Various reweight_entity() fixes

[Doug Smythies]

On 2026.02.12 11:29 Peter Zijlstra wrote:
> On Thu, Feb 12, 2026 at 06:16:11PM +0100, Peter Zijlstra wrote:
>> On Thu, Feb 12, 2026 at 12:59:43PM +0100, Peter Zijlstra wrote:
>>> On Thu, Feb 12, 2026 at 01:13:30PM +0530, K Prateek Nayak wrote:
>> 
>>>>     Enqueue cfs_rq: depth(1) weight(2144337920) nr_queued(2045) sum_w_vruntime(18343811230990336)    sum_weight(2144337920)
zero_vruntime(18337852274) sum_shift(0) avg_vruntime(18337852274)
>>>>     Dequeue cfs_rq: depth(1) weight(2144337920) nr_queued(2045) sum_w_vruntime(1303379968)           sum_weight(2143289344)
zero_vruntime(18354971669) sum_shift(0) avg_vruntime(18354971669)
>> 
>> After staring at waaay too many traces of my own, which confirm what
>> you're seeing, but didn't want to make any sense either...
>> 
>> ... I thinks I found it ...
>> 
>> Note that sum_weight, that has _just_ flipped bit 31 and thus turned
>> negative *if* it were a 32bit number. Every time, exactly at this point
>> things started to go sideways.
>> 
>> So I went looking for where this might be and I found the below.
>> 
>> My latest run has passed 0x8000000/(1024*1024) = 2048 tasks and is still
>> running. Numbers are still sane, fingers crossed.
>> 
>
> I made it all the way to 3k tasks on the one CPU and all is well.

I got to the full 20,000 X yes tasks on my test computer. All good.