Re: [Xen-devel] [PATCH v4 07/10] xen/arm: optee: add support for arbitrary shared memory

[Julien Grall <julien.grall@xxxxxxx>]

Hi,

On 3/20/19 7:37 PM, Volodymyr Babchuk wrote:
> Julien Grall writes:
> > Anyway, you should explain how you decide the placement of each
> > hypercall_preempt_check(). For instance, if the lists are quite big,
> > then you may want add a preempt check in the loop.
> I see your point there. Check in the loop would require additional
> logic. Is there any best practices? E.g. how often I should check for
> preemption? Every N iterations of loop, where N is...
It depends on how complex are each iteration of the loop. For instance, 
in the p2m code, we check preemption every 512 mappings freed (see 
relinquish_p2m_mapping).
> > The key point here is to document the choice even if you wrote it is
> > "random". This will help in the future if we need to revise preemption
> > choice.
> I'd prefer to do proper fix, if it does not require a big amount of
> work. Otherwise I'll add document the current state.
proper fix and preemption cannot be in the same sentence :). This is a 
judgment call based on the complexity of the code.
In the example I gave above, we decided arbitrarily to preempt every 512 
iterations. We didn't have any number but though 512 iterations was a 
good number.
I don't expect you to find the best place right now. I am only asking to 
document just we know the choice was "arbitrary".
Cheers,

--
Julien Grall

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