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Subject: Re: [PATCH 1/6] sched: migration changes for core scheduling
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     "Joel Fernandes (Google)" <joel@joelfernandes.org>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Tim Chen <tim.c.chen@linux.intel.com>,
        Vineeth Pillai <viremana@linux.microsoft.com>,
        Aaron Lu <aaron.lwe@gmail.com>,
        Aubrey Li <aubrey.intel@gmail.com>, tglx@linutronix.de,
        linux-kernel@vger.kernel.org, mingo@kernel.org,
        torvalds@linux-foundation.org, fweisbec@gmail.com,
        keescook@chromium.org, Phil Auld <pauld@redhat.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>, vineeth@bitbyteword.org,
        Chen Yu <yu.c.chen@intel.com>,
        Christian Brauner <christian.brauner@ubuntu.com>,
        Agata Gruza <agata.gruza@intel.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@intel.com>,
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        rostedt@goodmis.org, benbjiang@tencent.com,
        Alexandre Chartre <alexandre.chartre@oracle.com>,
        James.Bottomley@hansenpartnership.com, OWeisse@umich.edu,
        Dhaval Giani <dhaval.giani@oracle.com>, chris.hyser@oracle.com,
        Josh Don <joshdon@google.com>, Hao Luo <haoluo@google.com>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Aubrey Li <aubrey.li@intel.com>
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From:   "Li, Aubrey" <aubrey.li@linux.intel.com>
Message-ID: <9398a329-5989-0e3f-26d4-4193b25e7958@linux.intel.com>
Date:   Mon, 22 Mar 2021 21:17:10 +0800
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On 2021/3/22 20:56, Peter Zijlstra wrote:
> On Mon, Mar 22, 2021 at 08:31:09PM +0800, Li, Aubrey wrote:
>> Please let me know if I put cookie match check at the right position
>> in task_hot(), if so, I'll obtain some performance data of it.
>>
>> Thanks,
>> -Aubrey
>>
>> =======================================================
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 7f2fb08..d4bdcf9 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -1912,6 +1912,13 @@ static void task_numa_find_cpu(struct task_numa_env *env,
>>  		if (!cpumask_test_cpu(cpu, env->p->cpus_ptr))
>>  			continue;
>>  
>> +		/*
>> +		 * Skip this cpu if source task's cookie does not match
>> +		 * with CPU's core cookie.
>> +		 */
>> +		if (!sched_core_cookie_match(cpu_rq(cpu), env->p))
>> +			continue;
>> +
>>  		env->dst_cpu = cpu;
>>  		if (task_numa_compare(env, taskimp, groupimp, maymove))
>>  			break;
> 
> This one might need a little help too, I've not fully considered NUMA
> balancing though.
> 
>> @@ -6109,7 +6120,9 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>>  	for_each_cpu_wrap(cpu, cpus, target) {
>>  		if (!--nr)
>>  			return -1;
>> -		if (available_idle_cpu(cpu) || sched_idle_cpu(cpu))
>> +
>> +		if ((available_idle_cpu(cpu) || sched_idle_cpu(cpu)) &&
>> +		    sched_cpu_cookie_match(cpu_rq(cpu), p))
>>  			break;
>>  	}
>>  
> 
> This doesn't even apply... That code has changed.
> 
>> @@ -7427,6 +7440,14 @@ static int task_hot(struct task_struct *p, struct lb_env *env)
>>  
>>  	if (sysctl_sched_migration_cost == -1)
>>  		return 1;
>> +
>> +	/*
>> +	 * 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 1;
>> +
>>  	if (sysctl_sched_migration_cost == 0)
>>  		return 0;
>>  
> 
> Should work I think, but you've put it in a weird spot for breaking up
> that sysctl_sched_migration_cost thing. I'd have put it either in front
> or after that other SMT thing we have there.
> 

I did it on purpose.

If migration cost is huge, the task should not migrate, no matter the
cookie is matched or not. So have to after sysctl_sched_migration_cost == -1.

And if migration cost = 0 or delta < migrate cost , the task can be migrated,
but before migrate, We need to check whether cookie is matched or not. So before
sysctl_sched_migration_cost == 0.

Please correct me if I was wrong.

Thanks,
-Aubrey