linux-kernel - Re: [Patch v5 08/16] smt: Create cpu_smt_enabled static key for SMT specific code

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Message-ID: <6ed8faad-9c9b-78ac-d77f-50802b695bf0@linux.intel.com>
Date:   Mon, 19 Nov 2018 11:25:08 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Jiri Kosina <jikos@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Andi Kleen <ak@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Casey Schaufler <casey.schaufler@...el.com>,
        Asit Mallick <asit.k.mallick@...el.com>,
        Arjan van de Ven <arjan@...ux.intel.com>,
        Jon Masters <jcm@...hat.com>,
        Waiman Long <longman9394@...il.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [Patch v5 08/16] smt: Create cpu_smt_enabled static key for SMT
 specific code

Thomas,


>>  
>> +#ifdef CONFIG_SCHED_SMT
>> +
>> +extern struct static_key_false sched_smt_present;
>> +
>> +static inline bool cpu_smt_present(void)
>> +{
>> +	if (static_branch_unlikely(&sched_smt_present))
>> +		return true;
>> +	else
>> +		return false;
> 
> What's wrong with
> 
>        return static_branch_unlikely(&sched_smt_present);
> 
> ???
> 
> But that's just a stylistic nitpick. The real issue is that you prevent the
> mitigation when CONFIG_SCHED_SMT=n.
> 

Right. The sched_smt_present is just a scheduler construct and the sibling
cpu will still be brought online.  Scratch this.

Tim