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From:   Thomas Gleixner <tglx@linutronix.de>
To:     Dave Hansen <dave.hansen@intel.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     x86@kernel.org, Tom Lendacky <thomas.lendacky@amd.com>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Arjan van de Ven <arjan@linux.intel.com>,
        Huang Rui <ray.huang@amd.com>, Juergen Gross <jgross@suse.com>,
        Dimitri Sivanich <dimitri.sivanich@hpe.com>,
        Michael Kelley <mikelley@microsoft.com>,
        Wei Liu <wei.liu@kernel.org>, Pu Wen <puwen@hygon.cn>,
        Qiuxu Zhuo <qiuxu.zhuo@intel.com>,
        Sohil Mehta <sohil.mehta@intel.com>
Subject: Re: [patch V4 02/41] cpu/SMT: Make SMT control more robust against
 enumeration failures
In-Reply-To: <3b9518f5-8b92-1c24-286c-47bf9e8b8a2e@intel.com>
References: <20230814085006.593997112@linutronix.de>
 <20230814085112.149440843@linutronix.de>
 <3b9518f5-8b92-1c24-286c-47bf9e8b8a2e@intel.com>
Date:   Tue, 10 Oct 2023 14:18:47 +0200
Message-ID: <87r0m2oel4.ffs@tglx>
MIME-Version: 1.0
Content-Type: text/plain
Precedence: bulk

On Tue, Aug 15 2023 at 14:15, Dave Hansen wrote:
> On 8/14/23 01:53, Thomas Gleixner wrote:
>> -static inline bool cpu_smt_allowed(unsigned int cpu)
>> +static inline bool cpu_bootable(unsigned int cpu)
>>  {
>>  	if (cpu_smt_control == CPU_SMT_ENABLED)
>>  		return true;
>>  
>> +	if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
>> +		return true;
>
> I found this new pair of if()'s rather counterintuitive to read.
>
> The first one reads like:
>
> 	"If SMT is not supported, the CPU is always bootable"
>
> but "supported" could easily mean CONFIG_SMP==n (which is actually
> covered in the next case).  Would this be better named:
>
> 	CPU_SMT_NOT_ENUMERATED
> or
> 	CPU_SMT_NOT_DETECTED
>
> ?

Yes, no, maybe. I rather keep them as is because the strings which are
exposed via sysfs cannot be changed and are matching.

> 	/* Every CPU is bootable on non-SMT systems: */
> 	if (cpu_smt_control == CPU_SMT_NOT_DETECTED)
> 		return true;
>
> For the next one:
>
>> +	if (cpu_smt_control == CPU_SMT_NOT_IMPLEMENTED)
>> +		return true;
>
> This reads a bit like "SMT is not implemented" rather than "SMT controls
> are not implemented".  Maybe a comment would help:
>
> 	/* All CPUs are bootable if controls are not implemented: */

Sure.