Re: [PATCH] x86: Don't write io_apic ID if it is not changed

[Ingo Molnar]

* Eric W. Biederman <ebiederm@xxxxxxxxxxxx> wrote:

> Yinghai Lu <yinghai@xxxxxxxxxx> writes:
> 
> > For 32bit mptable path, setup_ids_from_mpc() always write io apic id
> > register, even there is no change needed.
> >
> > So try to do that when they are different bewteen reading out and
> > mptable
> 
> What is the advantage of not writing the value?

Just guessing, but if other OSs dont do it we might surprise buggy hardware 
[and trigger erratas in them], so this would be a standard 'dont touch the hw 
unless necessary' defensive move.

Similar bugs are not unprecedented.

Thanks,

	Ingo
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