Messages in this thread | | | Date | Fri, 30 Mar 2018 13:45:57 -0700 | From | Davidlohr Bueso <> | Subject | Re: [REVIEW][PATCH 11/11] ipc/sem: Fix semctl(..., GETPID, ...) between pid namespaces |
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On Fri, 30 Mar 2018, Eric W. Biederman wrote:
>Davidlohr Bueso <dave@stgolabs.net> 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
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