>> Early last year x86 changed their spinlock implementation to >> use a fair "ticket" system (just like the one at deli counter >> in the grocery store). Here is the same conversion for ia64. > > A naieve comment, but doesn't a desire to implement "fairness" suggest lock > contention that aught to be addressed? No, that's a good point. I was a bit surprised that the ticket patch went into x86 with so little fuss given the long standing attitude that the fix for lock contention problems was not to go tweaking the locking code to make it faster ... but to go and do possibly major surgery on the code that was using to locks to reduce the contention by changing the algorithm or the locking scope, or moving to lockless algorithms when possible. But the patch went in because the ticket locks were only very slightly slower in the uncontended case, and they did solve a real problem for a common two socket platform where the lack of fairness allowed the cores on one socket to freeze out the cores on the other socket for extremely long periods. I do have a data point for the performance of ticket locks on ia64. For kernel compiles (using "make -j12" on a 4-socket, 8-core, 16-thread system), the impact is in the noise. Mean time to build across 300 builds was 0.2% slower with ticket locks ... but the run to run variation on these builds was 1.6% (for +/- one standard deviation). -Tony -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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