[Intel-gfx] [PATCH 1/2] drm/i915: Pre-calculate engine context size

[Zhi Wang]

Uh...sorry for not mentioning that before:), and stolen memory is not my 
business. :(

Actually we root-caused it.

This is how we found this case:

The story is W driver directly allocated the ring buffer after the 
context image, and the context image size in W driver is 19 pages. GVT-g 
will do shadow context during submission, we copy 20 pages from guest 
context image, so you can see, an extra page is copied here as the 
context image size is actual 19 pages. The extra page belows to ring 
buffer. When guest updates that page with new commands during GVT-g 
executing the workload, the extra page ( which is ring buffer page) will 
be over-written with old content, since GVT-g will copy the shadow 
context (20 pages) back to guest at this time.

That's the full story. I send another email to Harsh. He should know if 
the context image size of CHV is also 19 pages.

Thanks,
Zhi.

于 04/26/17 17:52, Joonas Lahtinen 写道:
> On ke, 2017-04-26 at 17:10 +0800, Zhi Wang wrote:
>> Hi Joonas:
>>       Can you change GEN8_LR_CONTEXT_RENDER_SIZE = (19 * PAGE_SIZE)?
>> Then we don't need the hack in GVT-g. :P Actually it's 19 pages not
>> 20 pages on BDW.
> The exception is only made for BDW, not Gen8 overall. Has the change
> been verified for CHV too?
>
> Why hasn't a patch to fix above been sent for i915 in the past? Just
> like in the stolen memory disabling case, bugs should be root caused
> and then fixed, not just worked around quickly.
>
> Regards, Joonas