On Fri, 30 Mar 2018, Eric W. Biederman wrote:
Davidlohr Bueso <dave@xxxxxxxxxxxx> writes:I ran this on a 40-core (no ht) Westmere with two benchmarks. The first is Manfred's sysvsem lockunlock[1] program which uses _processes_ to, well, lock and unlock the semaphore. The options are a little unconventional, to keep the "critical region small" and the lock+unlock frequency high I added busy_in=busy_out=10. Similarly, to get the worst case scenario and have everyone update the same semaphore, a single one is used. Here are the results (pretty low stddev from run to run) for doing 100,000 lock+unlock. - 1 proc: * vanilla total execution time: 0.110638 seconds for 100000 loops * dirty total execution time: 0.120144 seconds for 100000 loops - 2 proc: * vanilla total execution time: 0.379756 seconds for 100000 loops * dirty total execution time: 0.477778 seconds for 100000 loops - 4 proc: * vanilla total execution time: 6.749710 seconds for 100000 loops * dirty total execution time: 4.651872 seconds for 100000 loops - 8 proc: * vanilla total execution time: 5.558404 seconds for 100000 loops * dirty total execution time: 7.143329 seconds for 100000 loops - 16 proc: * vanilla total execution time: 9.016398 seconds for 100000 loops * dirty total execution time: 9.412055 seconds for 100000 loops - 32 proc: * vanilla total execution time: 9.694451 seconds for 100000 loops * dirty total execution time: 9.990451 seconds for 100000 loops - 64 proc: * vanilla total execution time: 9.844984 seconds for 100032 loops * dirty total execution time: 10.016464 seconds for 100032 loops Lower task counts show pretty massive performance hits of ~9%, ~25% and ~30% for single, two and four/eight processes. As more are added I guess the overhead tends to disappear as for one you have a lot more locking contention going on.Can you check your notes on the 4 process case? As I read the 4 process case above it is ~30% improvement. Either that is a typo or there is the potential for quite a bit of noise in the test case.
Yeah, sorry that was a typo. Unlike the second benchmark I didn't have this one automated but it's always the vanilla kernel that outperforms the dirty. Thanks, Davidlohr -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
