RE: [PATCH v2] RISC-V: Probe misaligned access speed in parallel

[David Laight <David.Laight@ACULAB.COM>]

...
> > For probing alignment speed, you just care about running it on that
> > cpu. Correct ?
> 
> For this we care both about not migrating to other CPUs, and also
> secondarily minimizing disturbances while the test is being run.
> Usually I equate pre-emption with migration, but in this case I think
> the worker threads are bound to that CPU. So I'll keep the
> preempt_disable/enable where it is, since it's harmless for CPUs other
> than 0, but useful for 0. I also like it for readability as it
> highlights the critical section (as a reader, "is preemption disabled"
> would be one of my first questions when studying this).

You need to disable pre-emption to get any kind of meaningful answer.

But why do you need to run the test on more than the boot cpu?
If you've a heterogenous mix of cpu any code that looks at the answer
is going to behave incorrectly unless it has also disabled pre-emption
or is bound to a cpu.

One obvious use of the result is to setup some static branches.
But that assumes all cpu are the same.

	David

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