linux-kernel - Re: [PATCH v2 20/23] sched/cache: Add user control to adjust the parameters of cache-aware scheduling

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Message-ID: <968a52f0-3f64-4164-b7c3-c8d7bf61ebe2@intel.com>
Date: Tue, 16 Dec 2025 15:42:33 +0800
From: "Chen, Yu C" <yu.c.chen@...el.com>
To: Peter Zijlstra <peterz@...radead.org>, Tim Chen
	<tim.c.chen@...ux.intel.com>
CC: Ingo Molnar <mingo@...hat.com>, K Prateek Nayak <kprateek.nayak@....com>,
	"Gautham R . Shenoy" <gautham.shenoy@....com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Juri Lelli <juri.lelli@...hat.com>, "Dietmar
 Eggemann" <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, "Valentin
 Schneider" <vschneid@...hat.com>, Madadi Vineeth Reddy
	<vineethr@...ux.ibm.com>, Hillf Danton <hdanton@...a.com>, Shrikanth Hegde
	<sshegde@...ux.ibm.com>, Jianyong Wu <jianyong.wu@...look.com>, Yangyu Chen
	<cyy@...self.name>, Tingyin Duan <tingyin.duan@...il.com>, Vern Hao
	<vernhao@...cent.com>, Vern Hao <haoxing990@...il.com>, Len Brown
	<len.brown@...el.com>, Aubrey Li <aubrey.li@...el.com>, Zhao Liu
	<zhao1.liu@...el.com>, Chen Yu <yu.chen.surf@...il.com>, Adam Li
	<adamli@...amperecomputing.com>, Aaron Lu <ziqianlu@...edance.com>, Tim Chen
	<tim.c.chen@...el.com>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 20/23] sched/cache: Add user control to adjust the
 parameters of cache-aware scheduling

On 12/11/2025 1:02 AM, Peter Zijlstra wrote:
> On Wed, Dec 03, 2025 at 03:07:39PM -0800, Tim Chen wrote:
> 
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 466ba8b7398c..95bf080bbbf0 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -2436,9 +2436,11 @@ extern void migrate_enable(void);
>>   DEFINE_LOCK_GUARD_0(migrate, migrate_disable(), migrate_enable())
>>   
>>   #ifdef CONFIG_SCHED_CACHE
>> +DECLARE_STATIC_KEY_FALSE(sched_cache_on);
>> +
>>   static inline bool sched_cache_enabled(void)
>>   {
>> -	return false;
>> +	return static_branch_unlikely(&sched_cache_on);
>>   }
>>   #endif
>>   
>> diff --git a/kernel/sched/debug.c b/kernel/sched/debug.c
>> index 02e16b70a790..cde324672103 100644
>> --- a/kernel/sched/debug.c
>> +++ b/kernel/sched/debug.c
>> @@ -169,6 +169,53 @@ static const struct file_operations sched_feat_fops = {
>>   	.release	= single_release,
>>   };
>>   
>> +#ifdef CONFIG_SCHED_CACHE
>> +#define SCHED_CACHE_CREATE_CONTROL(name, max)			  \
>> +static ssize_t sched_cache_write_##name(struct file *filp,	  \
>> +					const char __user *ubuf,  \
>> +					size_t cnt, loff_t *ppos) \
>> +{								  \
>> +	char buf[16];						  \
>> +	unsigned int val;					  \
>> +	if (cnt > 15)						  \
>> +		cnt = 15;					  \
>> +	if (copy_from_user(&buf, ubuf, cnt))			  \
>> +		return -EFAULT;					  \
>> +	buf[cnt] = '\0';					  \
> 
> 
>> +	if (kstrtouint(buf, 10, &val))				  \
>> +		return -EINVAL;					  \
>> +	if (val > (max))						  \
>> +		return -EINVAL;					  \
>> +	llc_##name = val;					  \
>> +	if (!strcmp(#name, "enabled"))				  \
>> +		sched_cache_set(false);				  \
> 
> Oh gawd :-(
> 
> Please just write out all the various write methods and use
> kstrtoul_from_user() and kstrtobool_from_user() where applicable.
> 

OK, will do.

thanks,
Chenyu