[Intel-gfx] [PATCH v2] drm/i915/tgl: Add sysfs interface to control class-of-service

[Chris Wilson]

Quoting Prathap Kumar Valsan (2019-08-26 00:35:27)
> To provide shared last-level-cache isolation to cpu workloads running
> concurrently with gpu workloads, the gpu allocation of cache lines needs
> to be restricted to certain ways. Currently GPU hardware supports four
> class-of-service(CLOS) levels and there is an associated way-mask for
> each CLOS.
> 
> Hardware supports reading supported way-mask configuration for GPU using
> a bios pcode interface. The supported way-masks and the one currently
> active is communicated to userspace via a sysfs file--closctrl. Admin user
> can then select a new mask by writing the mask value to the file.

What impact does this have on inflight work? Do you need to drain the
submission queue, change the global registers, force an invalidation and
then restart? Can it be done from inside the GPU so that it is
serialised with on-going submission?
-Chris