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Subject: Re: [PATCH 1/2] sched/topology: Don't enable EAS on SMT systems
To:     Quentin Perret <qperret@google.com>,
        Valentin Schneider <valentin.schneider@arm.com>
Cc:     linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        morten.rasmussen@arm.com,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>, kernel-team@android.com
References: <20200226164118.6405-1-valentin.schneider@arm.com>
 <20200226164118.6405-2-valentin.schneider@arm.com>
 <20200227130001.GA107011@google.com>
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
Message-ID: <7ce12aa2-1925-f991-a85f-5bd81ba668fb@arm.com>
Date:   Thu, 27 Feb 2020 16:28:01 +0000
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On 27.02.20 13:00, Quentin Perret wrote:
> On Wednesday 26 Feb 2020 at 16:41:17 (+0000), Valentin Schneider wrote:
>> EAS already requires asymmetric CPU capacities to be enabled, and mixing
>> this with SMT is an aberration, but better be safe than sorry.
>>
>> Signed-off-by: Valentin Schneider <valentin.schneider@arm.com>
> 
> Acked-by: Quentin Perret <qperret@google.com>
> 
> Thanks,
> Quentin
> 
>> ---
>>  kernel/sched/topology.c | 4 ++++
>>  1 file changed, 4 insertions(+)
>>
>> diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c
>> index 00911884b7e7..76cd0a370b9a 100644
>> --- a/kernel/sched/topology.c
>> +++ b/kernel/sched/topology.c
>> @@ -360,6 +360,10 @@ static bool build_perf_domains(const struct cpumask *cpu_map)
>>  		goto free;
>>  	}
>>  
>> +	/* EAS definitely does *not* handle SMT */
>> +	if (sched_smt_active())

Can you add a pr_warn() and use the current comment as the warning
message? Since we have one for !Asym CPU capacity and !schedutil.

>> +		goto free;
>> +

[...]

There is this 'EAS can be used ...' list of currently 4 items in the
build_perf_domains() function header. You could include 'X. No SMT
support' there.
 ;-)