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    SubjectRE: [tip:x86/mm] x86/pat: Avoid contention on cpa_lock if possible
    Peter Zijlstra [mailto:a.p.zijlstra@chello.nl] wrote
    > On Wed, 2012-06-06 at 09:18 -0700, tip-bot for Shai Fultheim wrote:
    >
    > > [ I absolutely hate these locking patterns ... yet I have no better idea. Maybe the gents on Cc: ... ]
    > > Signed-off-by: Ingo Molnar <mingo@kernel.org>
    >
    > Oh yuck, this is vile..
    >
    > static struct static_key scale_mp_trainwreck = STATIC_KEY_INIT_FALSE;
    >
    > static DEFINE_SPINLOCK(_cpa_lock);
    >
    > static inline void cpa_lock(void)
    > {
    > if (static_key_false(&scale_mp_trainwreck))
    > return;
    >
    > spin_lock(&_cpa_lock);
    > }
    >
    > static inline void cpa_unlock(void)
    > {
    > if (static_key_false(&scale_mp_trainwreck))
    > return;
    >
    > spin_lock(&_cpa_lock);
    > }
    >
    > And then use cpa_{,un}lock(), and the scale-mp guys can
    > static_key_slow_inc(&scale_mp_trainwreck).
    >
    > [ and yes I hate those jump_label names ... but I'm not wanting
    > to go through another round of bike-shed painting. ]

    Looks pretty straight forward to do.
    We will try this route, as I'm concerned that synthetic CPUID bit will be kind of a global change for a pretty local consideration.

    Comments?

    (and we will also fix the other error pointed by Ingo - we are missing an include in this patch)

    Regards,
    Shai.


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