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Re: Refreshing cpu cache before atomic relaxed loads

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On Monday, 22 June 2015 21:30:04 UTC+2, itaj sherman  wrote:
> My question turned up while implementing spin-wait
> when a thread needs to wait for another thread to complete a short work,
> so short that locking/releasing a mutex might take longer than the work.
> The problem the way I see it is the standard does not explicitly define a
> clear way to refresh the cpu cache before re-loading an atomic variable.

The standard does not deal with CPU caches, or even CPUs for that matter.
The standard specifies an abstract machine, whose observable behaviour
every conforming implementation must emulate with respect to a well-formed
C++ program given to it. CPUs and caches are a detail internal to the
implementation; your C++ program cannot deal with that in a
standard-conforming, implementation-independent way. So the part of your
question regarding refreshing the cache is meaningless for this group.

With respect to "speed", the question is not very well formed. The speed of
what? Of every single iteration of the while loop? Is that even important?
Or the speed of the entire spin_wait_flag execution? Under what conditions?

Unless your formulate your speed measurement methodology, your question
cannot be answered. And if you do formulate your methodology, then you do
not need this group to answer your question, because you can use your
methodology to measure the speed, whatever it is.


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Refreshing cpu cache before atomic relaxed loads itaj sherman <itajsherman@googlemail.com> - 2015-06-22 14:22 -0600
  Re: Refreshing cpu cache before atomic relaxed loads via.usov@googlemail.com - 2015-06-25 14:32 -0600
  Re: Refreshing cpu cache before atomic relaxed loads itaj sherman <itajsherman@googlemail.com> - 2015-06-26 01:29 -0600

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