Re: [PATCH 1/6] sched: migration changes for core scheduling

["Li, Aubrey" <aubrey.li@linux.intel.com>]

Hi Peter,

On 2021/3/20 23:34, Peter Zijlstra wrote:
> On Fri, Mar 19, 2021 at 04:32:48PM -0400, Joel Fernandes (Google) wrote:
>> @@ -7530,8 +7543,9 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>>  	 * We do not migrate tasks that are:
>>  	 * 1) throttled_lb_pair, or
>>  	 * 2) cannot be migrated to this CPU due to cpus_ptr, or
>> -	 * 3) running (obviously), or
>> -	 * 4) are cache-hot on their current CPU.
>> +	 * 3) task's cookie does not match with this CPU's core cookie
>> +	 * 4) running (obviously), or
>> +	 * 5) are cache-hot on their current CPU.
>>  	 */
>>  	if (throttled_lb_pair(task_group(p), env->src_cpu, env->dst_cpu))
>>  		return 0;
>> @@ -7566,6 +7580,13 @@ int can_migrate_task(struct task_struct *p, struct lb_env *env)
>>  		return 0;
>>  	}
>>  
>> +	/*
>> +	 * Don't migrate task if the task's cookie does not match
>> +	 * with the destination CPU's core cookie.
>> +	 */
>> +	if (!sched_core_cookie_match(cpu_rq(env->dst_cpu), p))
>> +		return 0;
>> +
>>  	/* Record that we found atleast one task that could run on dst_cpu */
>>  	env->flags &= ~LBF_ALL_PINNED;
>>  
> 
> This one is too strong.. persistent imbalance should be able to override
> it.
> 

IIRC, this change can avoid the following scenario:

One sysbench cpu thread(cookieA) and sysbench mysql thread(cookieB) running
on the two siblings of core_1, the other sysbench cpu thread(cookieA) and
sysbench mysql thread(cookieB) running on the two siblings of core2, which
causes 50% force idle.

This is not an imbalance case.

Thanks,
-Aubrey