On Tue, May 6, 2014 at 8:33 AM, Jerome Glisse <j.glisse@xxxxxxxxx> wrote:
>
> So how can i solve the issue at hand. A device that has its own page
> table and can not mirror the cpu page table, nor can the device page
> table be updated atomicly from the cpu.
So? Just model it as a TLB.
Sure, the TLB is slow and crappy and is in external memory rather than
on-die, but it's still a TLB.
We have CPU's that do that kind of crazy thing (powerpc and sparc both
have these kinds of "in-memory TLB extensions" in addition to the
on-die TLB, they just call them "inverse page tables" to try to fool
people about what they are).
> I understand that we do not want to sleep when updating process cpu
> page table but note that only process that use the gpu would have to
> sleep. So only process that can actually benefit from the using GPU
> will suffer the consequences.
NO!
You don't get it. If a callback can sleep, then we cannot protect it
with a spinlock.
It doesn't matter if it only sleeps once in a millennium. It still
forces its crap on the rest of the system.
So there is no way in hell that we will allow that VM notifier crap. None.
And as I've mentioned, there is a correct place to slot this in, and
that correct way is the _only_ way to ever support future GPU's that
_do_ share direct access to the page tables.
So trying to do it any other way is broken _anyway_.
Linus
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