Why is the caption for this slide "Reduced contention leads to better performance"? The graphs are showing that adding more processors makes fine-grained locking faster, but adding processors should increase the opportunities for contention, no?
zhiyuany
@sgbowen, the execution time is the time of executing fixed number of operations, not the time per operation. Anyway, you cannot reduce the time per operation by adding more processors. The point is, adding processor does increase contention, but not incur too much overhead in fine-grained lock, so the total execution time decreases.
afa4
@sgbowen: You are right, adding more processors will increase the contention. But that contention will only be aggravated by coarse grained locks and hence fine-grained locks are seen to be performing much better with higher processor count.
yuel1
I believe the contention here is actually referring to contention for the lock. In course grained locking, there is a lot of contention for the lock, in fine grain locking, each individual lock has less contention.
Why is the caption for this slide "Reduced contention leads to better performance"? The graphs are showing that adding more processors makes fine-grained locking faster, but adding processors should increase the opportunities for contention, no?
@sgbowen, the execution time is the time of executing fixed number of operations, not the time per operation. Anyway, you cannot reduce the time per operation by adding more processors. The point is, adding processor does increase contention, but not incur too much overhead in fine-grained lock, so the total execution time decreases.
@sgbowen: You are right, adding more processors will increase the contention. But that contention will only be aggravated by coarse grained locks and hence fine-grained locks are seen to be performing much better with higher processor count.
I believe the contention here is actually referring to contention for the lock. In course grained locking, there is a lot of contention for the lock, in fine grain locking, each individual lock has less contention.