robert schrieb: > PS: Besides: what are speed costs of LOCK INC <mem> ?
That very much depends on the implementation. In http://gcc.gnu.org/ml/java/2001-03/msg00132.html Hans Boehm claims it's 15 cycles. The LOCK prefix itself asserts the lock# bus signal for the entire operation, meaning that the other processors can't perform memory operations during that time. On the P6, if the data is cacheable (for some Intel definition of this word), the lock# signal will not be asserted, just the cache gets locked. The LOCK prefix also causes any pending writes to be performed before the operation starts. So in the worst case, a LOCK INC will have to wait for pending writes, then will assert the lock# prefix, then perform a read and a write cycle memory cycle, with the increment processor cycle in-between. Assuming a 400MHz memory bus and a 4GHz processor, LOCK INC will take around 20 cycles, whereas a plain INC might get done in a single cycle or less (assuming pipelining and caching). Regards, Martin -- http://mail.python.org/mailman/listinfo/python-list
