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    Subject[PATCH 3.16 41/86] x86/Kconfig: Select SCHED_SMT if SMP enabled
    3.16.68-rc1 review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Thomas Gleixner <tglx@linutronix.de>

    commit dbe733642e01dd108f71436aaea7b328cb28fd87 upstream.

    CONFIG_SCHED_SMT is enabled by all distros, so there is not a real point to
    have it configurable. The runtime overhead in the core scheduler code is
    minimal because the actual SMT scheduling parts are conditional on a static
    key.

    This allows to expose the scheduler's SMT state static key to the
    speculation control code. Alternatively the scheduler's static key could be
    made always available when CONFIG_SMP is enabled, but that's just adding an
    unused static key to every other architecture for nothing.

    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Reviewed-by: Ingo Molnar <mingo@kernel.org>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Andy Lutomirski <luto@kernel.org>
    Cc: Linus Torvalds <torvalds@linux-foundation.org>
    Cc: Jiri Kosina <jkosina@suse.cz>
    Cc: Tom Lendacky <thomas.lendacky@amd.com>
    Cc: Josh Poimboeuf <jpoimboe@redhat.com>
    Cc: Andrea Arcangeli <aarcange@redhat.com>
    Cc: David Woodhouse <dwmw@amazon.co.uk>
    Cc: Tim Chen <tim.c.chen@linux.intel.com>
    Cc: Andi Kleen <ak@linux.intel.com>
    Cc: Dave Hansen <dave.hansen@intel.com>
    Cc: Casey Schaufler <casey.schaufler@intel.com>
    Cc: Asit Mallick <asit.k.mallick@intel.com>
    Cc: Arjan van de Ven <arjan@linux.intel.com>
    Cc: Jon Masters <jcm@redhat.com>
    Cc: Waiman Long <longman9394@gmail.com>
    Cc: Greg KH <gregkh@linuxfoundation.org>
    Cc: Dave Stewart <david.c.stewart@intel.com>
    Cc: Kees Cook <keescook@chromium.org>
    Link: https://lkml.kernel.org/r/20181125185004.337452245@linutronix.de
    [bwh: Backported to 3.16: CONFIG_SCHED_SMT depended on CONFG_X86_HT, but that
    also follows CONFIG_SMP]
    Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
    ---
    arch/x86/Kconfig | 8 +-------
    1 file changed, 1 insertion(+), 7 deletions(-)

    --- a/arch/x86/Kconfig
    +++ b/arch/x86/Kconfig
    @@ -798,13 +798,7 @@ config NR_CPUS
    approximately eight kilobytes to the kernel image.

    config SCHED_SMT
    - bool "SMT (Hyperthreading) scheduler support"
    - depends on X86_HT
    - ---help---
    - SMT scheduler support improves the CPU scheduler's decision making
    - when dealing with Intel Pentium 4 chips with HyperThreading at a
    - cost of slightly increased overhead in some places. If unsure say
    - N here.
    + def_bool y if SMP

    config SCHED_MC
    def_bool y
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