[PATCH 00/13] shadow page table support

Christian König deathsimple at vodafone.de
Tue Jul 26 08:27:09 UTC 2016

Am 26.07.2016 um 07:33 schrieb 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.

Correct, but we can't guarantee that for VM updates either.

> 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.

How about using a begin/end range of which parts of the BO needs to be 
backed up instead of a flag?

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

For shader BOs clearly not a good idea because they are rarely update 
and so backing them up every time would be a huge overhead.


> Regards,
> David Zhou

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