linux-kernel - Re: [PATCH] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in scx_ops

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Message-ID: <ef2f2766-ffed-4a35-a5e7-366483d48167@igalia.com>
Date: Wed, 8 Jan 2025 17:10:36 +0900
From: Changwoo Min <changwoo@...lia.com>
To: Andrea Righi <arighi@...dia.com>
Cc: tj@...nel.org, void@...ifault.com, kernel-dev@...lia.com,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched_ext: Replace rq_lock() to raw_spin_rq_lock() in
 scx_ops_bypass()

Hi Andrea,

Thank you for the review and suggestion!

On 25. 1. 8. 16:16, Andrea Righi wrote:
> Can we include the warning here? In this way people that are hitting the
> same warning can search for it and find this fix.
Sure. I will add the warning message.

> 
> Moreover, we can also add:
> 
> Fixes: 0e7ffff1b811 ("scx: Fix raciness in scx_ops_bypass()")
Will add this in the next version.

> Maybe we can also do this here since we're already holding the rq lock and
> irqs are disabled:
> 
> 		/* resched to restore ticks and idle state */
> 		if (cpu == smp_processor_id() || cpu_online(cpu))
> 			resched_curr(rq);
> 
>>   
>> -		rq_unlock(rq, &rf);
>> +		raw_spin_rq_unlock(rq);
>>   
> 
> And remove the following:
> 
>>   		/* resched to restore ticks and idle state */
>>   		resched_cpu(cpu);


This optimization makes sense. I will change it as suggested with
one minor change: I will flip the order in the if condition as
follows since cpu_online() is more commonly true:

  		/* resched to restore ticks and idle state */
  		if (cpu_online(cpu) || cpu == smp_processor_id())
  			resched_curr(rq);

Regards,
Changwoo Min