atomic operations in user space

Li Yang LeoLi at
Tue Aug 29 23:37:37 EST 2006

> This is exactly how it is supposed to work! That's why there is a loop
> in the atomic increment - you check if you still had the reservation
> after the transaction by checking the result from the stwcx, and if not,
> retry.

I surely know all the theories you mentioned clearly.  But please do
look at the case I gave.  Correct me if I missed anything.  Thanks

All the lwarx and stwcx operate on the same address.

> Task A		Task B
> lwarx				
> 			......
> 			lwarx
> 			stwcx

// RESERVATION cleared
> 			.....
> 			.....
> 			lwarx

// Get RESERVATION again
> stwcx				

//Note here: RESERVATION is valid, address is the same.
So the result is commited, no retry for task A

> .....
> 			stwcx
//RESERVATION is cleared, retry atomic op for task B

Please be noted that reservation is only identified by reservation bit
and address operated on.  So different lwarx's on the same address,
may be considered as the same reservation.

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