[ ... ]
> (my 8-way SMP box appears to be just fine after this change, under heavy
> load. dbench numbers are visibly up, 252MB/sec instead of 242MB/sec)
>
> i'm really happy about this - there are tons of places that are using
> spin_unlock, and this effectively cuts the cost of spinlocks into half.
Hmmm... Could it be that we are just playing too much with spinlocks. ;)
Even if the simple 'mov' may ensure other processors to have a consistent
view of the spinlock, it does not prevent the CPU that unlocks from
playing with speculative execution around the 'unlock' and perform
speculative reads for example. Without a minimal serialization this stuff
does not seem safe to me, or at least not for ever.
Gérard.
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