Re: [Question]: try to fix contention between expire_timers and try_to_del_timer_sync

[Vikram Mulukutla <markivx@codeaurora.org>]

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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