[PATCH 00/13] shadow page table support

[zhoucm1]

On 2016年07月26日 10:40, zhoucm1 wrote:
> 1. We add an optional "shadow" flag so that when a BO in VRAM is 
> allocated we also allocate a shadow BO in GART.
>
> 2. We have another "backup" flag that says on the next command 
> submission the BO is backed up from VRAM to GART before that submission.
>
> 3. We set the shadow flag for VM PD/PT BOs and every time we modify 
> them set the backup flag so they get backed up on next CS.
>
> 4. We add an IOCTL to allow setting the backup flag from userspace so 
> that we can trigger another backup even after the first CS. 
When I'm trying it and thinking more, a general shadow BO indeed be a 
sense way, but backup flag seems not necessary, mainly two reasons:
1. we cannot make sure backup job is completed when gpu reset happens.
2. backup flag is to copy the whole BO, which seems overhead. If we 
update shadow BO along with BO in real time, e.g. PD/PT, we could only 
update some ptes not the entire BO.

So can we assume shadow BO always needed to backup if shadow flag is set?

Regards,
David Zhou