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Message-ID: <3f6935de-d80f-0aa0-efd8-94a1076ce8d3@bytedance.com>
Date:   Thu, 20 Oct 2022 14:35:24 +0800
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Subject: Re: [RESEND] sched/fair: Add min_ratio for cfs bandwidth_control
To:     Tejun Heo <tj@kernel.org>
Cc:     linux-kernel@vger.kernel.org, htejun@gmail.com
References: <20221019031551.24312-1-zhouchuyi@bytedance.com>
 <Y1BqT59ovFitahJa@slm.duckdns.org>
From:   Chuyi Zhou <zhouchuyi@bytedance.com>
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在 2022/10/20 05:21, Tejun Heo 写道:
> Hello,
> 
> On Wed, Oct 19, 2022 at 11:15:51AM +0800, Chuyi Zhou wrote:
>> Tasks may be throttled when holding locks for a long time by current
>> cfs bandwidth control mechanism once users set a too small quota/period
>> ratio, which can result whole system get stuck[1].
>>
>> In order to prevent the above situation from happening, this patch adds
>> sysctl_sched_cfs_bandwidth_min_ratio in /proc/sys/kernel, which indicates
>> the minimum percentage of quota/period users can set. The default value is
>> zero and users can set quota and period without triggering this constraint.
>>
>> Link[1]:https://lore.kernel.org/lkml/5987be34-b527-4ff5-a17d-5f6f0dc94d6d@huawei.com/T/
>> Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com>
>> Suggested-by: Abel Wu <wuyun.abel@bytedance.com>
> 
> This is a bit of a bandaid. I think what we really need to do is only
> throttling when running in userspace. In kernel space, it should just keep
> accumulating used cycles as debt which should be paid back before userspace
> code can run again so that we don't throttle at random places in the kernel.
> 
> Thanks.
> 
Got it. Thanks for your advice.
Chuyi Zhou