Volatile vs Non-Volatile Spin Locks on SMP.

[<multisyncfe991@hotmail.com>]

Hello,

By using volatile keyword for spin lock defined by in spinlock_t, it seems 
Linux choose to always
reload the value of spin locks from cache instead of using the content from 
registers. This may be
helpful for synchronization between multithreads in a single CPU.

I use two Xeon cpus with HyperThreading being disabled on both cpus. I think 
the MESI
protocol will enforce the cache coherency and update the spin lock value 
automatically between
these two cpus. So maybe we don't need to use the volatile any more, right?

Based on this, I rebuilt the Intel e1000 Gigabit network card driver with 
volatile being removed,
but I didn't notice any performance improvement.

Any idea about this,

Thanks a lot,

Liang



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