Re: [PATCH 4/7] drm/i915: always pin lrc context for vgpu with Intel GVT-g

[Zhiyuan Lv <zhiyuan.lv@intel.com>]

Hi Chris,

On Thu, Aug 20, 2015 at 09:36:00AM +0100, Chris Wilson wrote:
> On Thu, Aug 20, 2015 at 03:45:21PM +0800, Zhiyuan Lv wrote:
> > Intel GVT-g will perform EXECLIST context shadowing and ring buffer
> > shadowing. The shadow copy is created when guest creates a context.
> > If a context changes its LRCA address, the hypervisor is hard to know
> > whether it is a new context or not. We always pin context objects to
> > global GTT to make life easier.
> 
> Nak. Please explain why we need to workaround a bug in the host. We
> cannot pin the context as that breaks userspace (e.g. synmark) who can
> and will try to use more contexts than we have room.

This change is only for i915 running inside a VM. Host i915 driver's
behavior will not be impacted.

The reason we want to pin context is that our hypervisor identifies
guest contexts with their LRCA, and need LRCA unchanged during
contexts' life cycle so that shadow copy of contexts can easily find
their counterparts. If we cannot pin them, we have to consider more
complicated shadow implementation ...

BTW Chris, are there many apps like synmark that may used up GGTT with
contexts if they are all pinned? Thanks!

Regards,
-Zhiyuan

> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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