linux-kernel - Re: [Patch v4 08/18] sched: Deprecate sched_smt_present and use cpu_smt

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Message-ID: <e6b4af48-d848-8567-5927-745bbf6a388b@linux.intel.com>
Date:   Fri, 9 Nov 2018 14:08:43 -0800
From:   Tim Chen <tim.c.chen@...ux.intel.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jiri Kosina <jikos@...nel.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        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 v4 08/18] sched: Deprecate sched_smt_present and use
 cpu_smt_enabled static key

Thomas,

> 
>> The cpu_smt_enabled static key serves identical purpose as cpu_smt_enabled
> 
> That doesn't make any sense.
> 
>> to enable SMT specific code.
>>
>> This patch replaces sched_smt_present in the scheduler with
>> cpu_smt_enabled and deprecate sched_smt_present.
> 
> It's not deprecating it, it's replacing and removing it and thereby
> breaking all architectures which select SCHED_SMT except x86.

But the cpu_smt_enabled key is not x86 specific.  It is set and
defined in generic kernel/cpu.c and include/linux/cpu.h and available
for all architectures.

Why would it break other architectures?  I am missing something?

Thanks.

Tim