Re: [PATCH v2 2/5] sched_ext: Manage the validity of scx_rq_clock

[Changwoo Min <changwoo@igalia.com>]

Hello Peter,

On 24. 12. 2. 18:58, Peter Zijlstra wrote:
> On Mon, Dec 02, 2024 at 01:38:46PM +0900, Changwoo Min wrote:
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index 95e40895a519..ab8015c8cab4 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -789,6 +789,7 @@ static void update_rq_clock_task(struct rq *rq, s64 delta)
>>   void update_rq_clock(struct rq *rq)
>>   {
>>   	s64 delta;
>> +	u64 clock;
>>   
>>   	lockdep_assert_rq_held(rq);
>>   
>> @@ -800,11 +801,14 @@ void update_rq_clock(struct rq *rq)
>>   		SCHED_WARN_ON(rq->clock_update_flags & RQCF_UPDATED);
>>   	rq->clock_update_flags |= RQCF_UPDATED;
>>   #endif
>> +	clock = sched_clock_cpu(cpu_of(rq));
>> +	scx_rq_clock_update(rq, clock);
> 
> This adds a write to a second cacheline for *everyone* always.
> 
> Please don't do that.
> 

Thank you for the suggestion! I will update the flags only when
the scx is enabled by checking it inside the
scx_rq_clock_update() and scx_rq_clock_stale() functions.

Regards,
Changwoo Min