On 02/21/2014 11:57 AM, Tejun Heo wrote:
Yo,
On Fri, Feb 21, 2014 at 11:53:46AM -0500, Peter Hurley wrote:
Ok, I can do that. But AFAIK it'll have to be an smp_rmb(); there is
no mb__after unlock.
We do have smp_mb__after_unlock_lock().
[ After thinking about it some, I don't think preventing speculative
writes before clearing PENDING if useful or necessary, so that's
why I'm suggesting only the rmb. ]
But smp_mb__after_unlock_lock() would be cheaper on most popular
archs, I think.
smp_mb__after_unlock_lock() is only for ordering memory operations
between two spin-locked sections on either the same lock or by
the same task/cpu. Like:
i = 1
spin_unlock(lock1)
spin_lock(lock2)
smp_mb__after_unlock_lock()
j = 1
This guarantees that the store to j happens after the store to i.
Without it, a cpu can
spin_lock(lock2)
j = 1
i = 1
spin_unlock(lock1)
Regards,
Peter Hurley
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