linux-kernel - Re: [PATCH 2/2] sched/fair: set burst to zero when set max to cpu.max

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Date: Wed, 29 May 2024 14:20:45 +0800
From: Cheng Yu <serein.chengyu@...wei.com>
To: Benjamin Segall <bsegall@...gle.com>
CC: <mingo@...hat.com>, <peterz@...radead.org>, <juri.lelli@...hat.com>,
	<vincent.guittot@...aro.org>, <dietmar.eggemann@....com>,
	<rostedt@...dmis.org>, <mgorman@...e.de>, <bristot@...hat.com>,
	<vschneid@...hat.com>, <changhuaixin@...ux.alibaba.com>,
	<shanpeic@...ux.alibaba.com>, <dtcccc@...ux.alibaba.com>, <tj@...nel.org>,
	<linux-kernel@...r.kernel.org>, <zhangqiao22@...wei.com>,
	<judy.chenhui@...wei.com>, <yusongping@...wei.com>, <zhaowenhui8@...wei.com>,
	<liaoqixin@...wei.com>
Subject: Re: [PATCH 2/2] sched/fair: set burst to zero when set max to cpu.max

On 2024/5/29 7:10, Benjamin Segall wrote:
> Cheng Yu <serein.chengyu@...wei.com> writes:
> 
>> In the cgroup v2 cpu subsystem, assuming we have a cgroup named 'test',
>> and we set cpu.max and cpu.max.burst:
>>     # echo 1000000 > /sys/fs/cgroup/test/cpu.max
>>     # echo 1000000 > /sys/fs/cgroup/test/cpu.max.burst
>>
>> Next we remove the restriction on cfs bandwidth:
>>     # echo max > /sys/fs/cgroup/test/cpu.max
>>     # cat /sys/fs/cgroup/test/cpu.max
>>     max 100000
>>     # cat /sys/fs/cgroup/test/cpu.max.burst
>>     1000000
>>
>> Now we expect that the value of burst should be 0. When the burst is 0,
>> it means that the restriction on burst is cancelled.
>>
>> Fixes: f4183717b370 ("sched/fair: Introduce the burstable CFS controller")
>> Reported-by: Qixin Liao <liaoqixin@...wei.com>
>> Signed-off-by: Cheng Yu <serein.chengyu@...wei.com>
> 
> Yeah, makes sense. My general assumption would be to put these in one
> patch, but if there's a convention to separate v1 and v2 that I've
> missed, I have no opinion.
> 
> Reviewed-by: Ben Segall <bsegall@...gle.com>
> 
Thanks for the advice. I will submit a v2 patch that includes both cgroup v1 and v2 modification.

>> ---
>>  kernel/sched/core.c | 5 ++++-
>>  1 file changed, 4 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>> index e9198e30bb74..982d357b3983 100644
>> --- a/kernel/sched/core.c
>> +++ b/kernel/sched/core.c
>> @@ -11414,8 +11414,11 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
>>  	int ret;
>>  
>>  	ret = cpu_period_quota_parse(buf, &period, &quota);
>> -	if (!ret)
>> +	if (!ret) {
>> +		if (quota == RUNTIME_INF)
>> +			burst = 0;
>>  		ret = tg_set_cfs_bandwidth(tg, period, quota, burst);
>> +	}
>>  	return ret ?: nbytes;
>>  }
>>  #endif