Hi,
On Wed, Jun 06, 2012 at 06:18:12PM -0400, Shai Fultheim (Shai@xxxxxxxxxxx) wrote:
> Peter Zijlstra [mailto:a.p.zijlstra@xxxxxxxxx] 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@xxxxxxxxxx>
> >
> > 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?
The synthetic CPUID bit approach has the advantage of setting this bit
from the platform initialization code independently (in this case, in
vsmp_64.c) instead of calling platform specific functions from
pageattr.c (such as is_vsmp_box()) or exporting the static_key variable.
We'll give this a shot and send a revised patch after testing it.
Sounds good?
Thanks,
Ido.
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