Benjamin Herrenschmidt wrote:
On Wed, 2013-12-11 at 17:29 +1100, Michael Ellerman wrote:
It would be nice if you could make an assertion about what the state of HMT
handling should be once your patch is applied.
I think it's:
* The kernel should use HMT_MEDIUM_LOW as it's "default" priority
* The kernel should use HMT_LOW as it's "low" priority
Which would imply:
* The kernel should not use HMT_MEDIUM anywhere ..
* Nor should it use any of the other higher HMT modes.
Do you agree?
Not entirely. HT_MEDIUM might still be used by the kernel, in places where a
priority higher than the default is required.
The reason I ask is I still see HMT_MEDIUM used in a few places, and it's not
clear to me if that is correct.
HMT_MEDIUM used to be our default no ?
Yes, but I am not sure that all references to HMT_MEDIUM were references to the
default kernel priority.
Also there's an open question... when doing things with interrupts off
(or worse, in real mode) such as some KVM hcalls etc... should we on the
contrary boost up to limit interrupt latency ?
Yes. I think that there are cases when one should consider using HT_MEDIUM.
Shouldn't we define a new macro HMT_DEFAULT, to identify explicitely where the
default priority is required?
Philippe
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