linux-kernel - Re: [patch 10/24] sched/smt: Expose sched_smt

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Date:   Wed, 21 Nov 2018 21:41:10 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     LKML <linux-kernel@...r.kernel.org>
cc:     x86@...nel.org, Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Jiri Kosina <jkosina@...e.cz>,
        Tom Lendacky <thomas.lendacky@....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>,
        Greg KH <gregkh@...uxfoundation.org>,
        Dave Stewart <david.c.stewart@...el.com>,
        Kees Cook <keescook@...omium.org>
Subject: Re: [patch 10/24] sched/smt: Expose sched_smt_present static key

On Wed, 21 Nov 2018, Thomas Gleixner wrote:

> Make the scheduler's 'sched_smt_present' static key globaly available, so
> it can be used in the x86 speculation control code.
> 
> Provide a query function and a stub for the CONFIG_SMP=n case.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/sched/topology.h |    9 +++++++++
>  kernel/sched/sched.h           |    3 ---
>  2 files changed, 9 insertions(+), 3 deletions(-)
> 
> --- a/include/linux/sched/topology.h
> +++ b/include/linux/sched/topology.h
> @@ -34,10 +34,19 @@
>  #define SD_NUMA			0x4000	/* cross-node balancing */
>  
>  #ifdef CONFIG_SCHED_SMT
> +extern struct static_key_false sched_smt_present;
> +
> +static __always_inline bool sched_smt_active(void)
> +{
> +	return static_branch_likely(&sched_smt_present);

0day just told me that this breaks ia64.

/me goes to fix