linux-kernel - Re: [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs

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Message-ID: <87o7ln849u.ffs@tglx>
Date:   Sat, 10 Jun 2023 22:13:17 +0200
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Michael Ellerman <mpe@...erman.id.au>, linux-kernel@...r.kernel.org
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-arch@...r.kernel.org,
        ldufour@...ux.ibm.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        mingo@...hat.com, x86@...nel.org
Subject: Re: [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs

On Sat, Jun 10 2023 at 22:09, Thomas Gleixner wrote:

> On Thu, May 25 2023 at 01:56, Michael Ellerman wrote:
>> There is a hook which allows arch code to control how many threads per
>
> Can you please write out architecture in changelogs and comments?
>
> I know 'arch' is commonly used but while my brain parser tolerates
> 'arch_' prefixes it raises an exception on 'arch' in prose as 'arch' is
> a regular word with a completely different meaning. Changelogs and
> comments are not space constraint.
>
>> @@ -2505,20 +2505,38 @@ __store_smt_control(struct device *dev, struct device_attribute *attr,
>>  	if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
>>  		return -ENODEV;
>>  
>> -	if (sysfs_streq(buf, "on"))
>> +	if (sysfs_streq(buf, "on")) {
>>  		ctrlval = CPU_SMT_ENABLED;
>> -	else if (sysfs_streq(buf, "off"))
>> +		num_threads = cpu_smt_max_threads;
>> +	} else if (sysfs_streq(buf, "off")) {
>>  		ctrlval = CPU_SMT_DISABLED;
>> -	else if (sysfs_streq(buf, "forceoff"))
>> +		num_threads = 1;
>> +	} else if (sysfs_streq(buf, "forceoff")) {
>>  		ctrlval = CPU_SMT_FORCE_DISABLED;
>> -	else
>> +		num_threads = 1;
>> +	} else if (kstrtoint(buf, 10, &num_threads) == 0) {
>> +		if (num_threads == 1)
>> +			ctrlval = CPU_SMT_DISABLED;
>> +		else if (num_threads > 1 && topology_smt_threads_supported(num_threads))

Why does this not simply check cpu_smt_max_threads?

		else if (num_threads > 1 && num_threads <= cpu_smt_max_threads)

cpu_smt_max_threads should have been established already, no?

Thanks,

        tglx