[Intel-gfx] [RFCv2 10/14] drm/i915: update PDPs by condition when submit the LRC context

[Wang, Zhi A]

-----Original Message-----
From: Tian, Kevin 
Sent: Wednesday, February 24, 2016 4:50 PM
To: Wang, Zhi A; intel-gfx at lists.freedesktop.org; igvt-g at lists.01.org
Cc: Lv, Zhiyuan; Niu, Bing; Song, Jike; daniel.vetter at ffwll.ch; Cowperthwaite, David J; chris at chris-wilson.co.uk; joonas.lahtinen at linux.intel.com
Subject: RE: [RFCv2 10/14] drm/i915: update PDPs by condition when submit the LRC context

> From: Wang, Zhi A
> Sent: Thursday, February 18, 2016 7:42 PM
> 
> Previously the PDPs inside the ring context are updated at:
> 
> - When populate a LRC context
> - Before submitting a LRC context (only for 32 bit PPGTT, as the amount
> of used PDPs may change)
> 
> This patch postpones the PDPs upgrade to submission time, and will update
> it by condition if the PPGTT is 48b. Under GVT-g, one GVT context will be
> used by different guest, the PPGTT instance related to the context might
> be changed before the submission time. And this patch gives GVT context
> a chance to load the new PPGTT instance into an initialized context.

Could you elaborate why we share one GVT context across different guest?
A natural thought is that we'll create one GVT context per every guest
context...

[Zhi] We don't have context creation/destroy notification in guest i915 driver.
Because in our implementation we need an unique context id to anchor the
relationship between shadow context and guest context, while i915 uses GGTT
address as context id. In each context pin/unpin, the context id may be changes.

So it's not necessary to allocate multiple GVT context here. 

Thanks
Kevin