[Info-vax] Volatile, was: Re: yet another sys$qiow question

[Stephen Hoffman]

On 2015-08-29 01:08:36 +0000, David Froble said:

> Tying up a modern CPU, or CPUs, with tight loops seems conta-indicated to me.

Depends.  Is there something better that the core could be doing?   If 
not, then spin.  Used to be CPUs were scarce resources.

Is releasing and flushing the caches and the translation buffers and 
rescheduling something else going to be a smaller or a bigger hit?

Now, eight or sixteen cores per socket is becoming commonplace, and 
with something like the forthcoming Knights Landing (72 cores per 
socket) chip...

Even OpenVMS itself implements and uses spin-waiting — for what are 
hopefully short intervals — as that's the least disruptive approach; 
spinlocks.


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