Re: [PATCH v2] sched/fair: set burst to 0 when remove the restriction on cfs bandwidth

["zhaowenhui (A)" <zhaowenhui8@huawei.com>]

> Hi,
> 
> On 2024/7/9 2:08, Tejun Heo wrote:
>> Hello,
>>
>> On Mon, Jul 08, 2024 at 08:00:53PM +0800, Cheng Yu wrote:
>>> From: Zhao Wenhui <zhaowenhui8@huawei.com>
>>>
>>> In the cpu subsystem of cgroup v1 and v2, we set the restriction on cfs
>>> bandwidth by setting the quota and burst value. Later, when we remove
>>> the restriction by setting the quota to the default value, the burst
>>> value should also be forced to the its default value of zero.
>>
>> Explaining a bit why burst value should become zero can be helpful - ie.
>> what happens when quota is not set but burst is limited?
> 
> When the restriction on cfs bandwidth is removed, the purpose of setting
> burst value to zero is to avoid ambiguity.
> 
>>
>> ...
>>> @@ -10840,6 +10840,12 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota,
>>>   				     burst + quota > max_cfs_runtime))
>>>   		return -EINVAL;
>>>   
>>> +	/*
>>> +	 * Ensure burst equals to zero when quota is -1.
>>> +	 */
>>> +	if (quota == RUNTIME_INF && burst)
>>> +		return -EINVAL;
>>
>> This happening would be a bug, right? Would it make more sense to use
>> WARN_ON_ONCE()?
> 
> As Vishal Chourasia mentioned, it can prevent setting excessively large
> burst value. Using WARN_ON_ONCE() does not have this effect.
> 
>>
>> Thanks.
>>
> 
> Thanks
> --
> Cheng Yu

Friendly ping. Any more question about this patch?

Regards,
Zhao wenhui