Messages in this thread | | | Date | Wed, 5 Dec 2007 17:47:23 +0100 | From | Ingo Molnar <> | Subject | Re: Possible bug from kernel 2.6.22 and above, 2.6.24-rc4 |
| |
* Jie Chen <chen@jlab.org> wrote:
>> the moment you saturate the system a bit more, the numbers should >> improve even with such a ping-pong test. > > You are right. If I manually do load balance (bind unrelated processes > on the other cores), my test code perform as well as it did in the > kernel 2.6.21.
so right now the results dont seem to be too bad to me - the higher overhead comes from two threads running on two different cores and incurring the overhead of cross-core communications. In a true spread-out workloads that synchronize occasionally you'd get the same kind of overhead so in fact this behavior is more informative of the real overhead i guess. In 2.6.21 the two threads would stick on the same core and produce artificially low latency - which would only be true in a real spread-out workload if all tasks ran on the same core. (which is hardly the thing you want on openmp)
In any case, if i misinterpreted your numbers or if you just disagree, or if have a workload/test that shows worse performance that it could/should, let me know.
Ingo
| |