Messages in this thread |  | | Date | Fri, 25 Aug 2017 13:25:42 -0700 | From | Vikram Mulukutla <> | Subject | Re: [Question]: try to fix contention between expire_timers and try_to_del_timer_sync |
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On 2017-08-25 12:48, Vikram Mulukutla wrote:
> > If I understand the code correctly, the upper 32 bits of an ARM64 > virtual > address will overflow when 1 is added to it, and so we'll keep WFE'ing > on > every subsequent cpu_relax invoked from the same PC, until we cross the > hard-coded threshold, right? >
Oops, misread that. Second time we enter cpu_relax from the same PC, we do a WFE. Then we stop doing the WFE until we hit the threshold using the per-cpu counter. So with a higher threshold, we wait for more cpu_relax() calls before starting the WFE again.
So a lower threshold implies we should hit WFE branch sooner. It seems that since my test keeps the while loop going for a full 5 seconds, a lower threshold will obviously result in more WFEs and lower the lock-acquired-count.
I guess we want a high threshold but not so high that the little CPU has to wait a while before the big CPU counts up to the threshold, is that correct?
Thanks, Vikram
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