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

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Date:   Sun, 21 Mar 2021 21:34:00 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>
Cc:     Nishanth Aravamudan <naravamudan@...italocean.com>,
        Julien Desfossez <jdesfossez@...italocean.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Vineeth Pillai <viremana@...ux.microsoft.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, mingo@...nel.org,
        torvalds@...ux-foundation.org, fweisbec@...il.com,
        keescook@...omium.org, Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, vineeth@...byteword.org,
        Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
        rostedt@...dmis.org, benbjiang@...cent.com,
        Alexandre Chartre <alexandre.chartre@...cle.com>,
        James.Bottomley@...senpartnership.com, OWeisse@...ch.edu,
        Dhaval Giani <dhaval.giani@...cle.com>, chris.hyser@...cle.com,
        Josh Don <joshdon@...gle.com>, Hao Luo <haoluo@...gle.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Aubrey Li <aubrey.li@...el.com>
Subject: Re: [PATCH 1/6] sched: migration changes for core scheduling

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