[Intel-gfx] [PATCH 5/6] drm/i915: Expose RPCS (SSEU) configuration to userspace

[Chris Wilson]

Quoting Tvrtko Ursulin (2018-09-17 12:30:57)
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> We want to allow userspace to reconfigure the subslice configuration for
> its own use case. To do so, we expose a context parameter to allow
> adjustment of the RPCS register stored within the context image (and
> currently not accessible via LRI). If the context is adjusted before
> first use, the adjustment is for "free"; otherwise if the context is
> active we flush the context off the GPU (stalling all users) and forcing
> the GPU to save the context to memory where we can modify it and so
> ensure that the register is reloaded on next execution.
> 
> The overhead of managing additional EU subslices can be significant,
> especially in multi-context workloads. Non-GPGPU contexts should
> preferably disable the subslices it is not using, and others should
> fine-tune the number to match their workload.
> 
> We expose complete control over the RPCS register, allowing
> configuration of slice/subslice, via masks packed into a u64 for
> simplicity. For example,
> 
>         struct drm_i915_gem_context_param arg;
>         struct drm_i915_gem_context_param_sseu sseu = { .class = 0,
>                                                         .instance = 0, };
> 
>         memset(&arg, 0, sizeof(arg));
>         arg.ctx_id = ctx;
>         arg.param = I915_CONTEXT_PARAM_SSEU;
>         arg.value = (uintptr_t) &sseu;
>         if (drmIoctl(fd, DRM_IOCTL_I915_GEM_CONTEXT_GETPARAM, &arg) == 0) {
>                 sseu.packed.subslice_mask = 0;
> 
>                 drmIoctl(fd, DRM_IOCTL_I915_GEM_CONTEXT_SETPARAM, &arg);
>         }
> 
> could be used to disable all subslices where supported.
> 
> v2: Fix offset of CTX_R_PWR_CLK_STATE in intel_lr_context_set_sseu() (Lionel)
> 
> v3: Add ability to program this per engine (Chris)
> 
> v4: Move most get_sseu() into i915_gem_context.c (Lionel)
> 
> v5: Validate sseu configuration against the device's capabilities (Lionel)
> 
> v6: Change context powergating settings through MI_SDM on kernel context (Chris)
> 
> v7: Synchronize the requests following a powergating setting change using a global
>     dependency (Chris)
>     Iterate timelines through dev_priv.gt.active_rings (Tvrtko)
>     Disable RPCS configuration setting for non capable users (Lionel/Tvrtko)
> 
> v8: s/union intel_sseu/struct intel_sseu/ (Lionel)
>     s/dev_priv/i915/ (Tvrtko)
>     Change uapi class/instance fields to u16 (Tvrtko)
>     Bump mask fields to 64bits (Lionel)
>     Don't return EPERM when dynamic sseu is disabled (Tvrtko)
> 
> v9: Import context image into kernel context's ppgtt only when
>     reconfiguring powergated slice/subslices (Chris)
>     Use aliasing ppgtt when needed (Michel)
> 
> Tvrtko Ursulin:
> 
> v10:
>  * Update for upstream changes.
>  * Request submit needs a RPM reference.
>  * Reject on !FULL_PPGTT for simplicity.
>  * Pull out get/set param to helpers for readability and less indent.
>  * Use i915_request_await_dma_fence in add_global_barrier to skip waits
>    on the same timeline and avoid GEM_BUG_ON.
>  * No need to explicitly assign a NULL pointer to engine in legacy mode.
>  * No need to move gen8_make_rpcs up.
>  * Factored out global barrier as prep patch.
>  * Allow to only CAP_SYS_ADMIN if !Gen11.
> 
> v11:
>  * Remove engine vfunc in favour of local helper. (Chris Wilson)
>  * Stop retiring requests before updates since it is not needed
>    (Chris Wilson)
>  * Implement direct CPU update path for idle contexts. (Chris Wilson)
>  * Left side dependency needs only be on the same context timeline.
>    (Chris Wilson)
>  * It is sufficient to order the timeline. (Chris Wilson)
>  * Reject !RCS configuration attempts with -ENODEV for now.
> 
> v12:
>  * Rebase for make_rpcs.
> 
> v13:
>  * Centralize SSEU normalization to make_rpcs.
>  * Type width checking (uAPI <-> implementation).
>  * Gen11 restrictions uAPI checks.
>  * Gen11 subslice count differences handling.
>  Chris Wilson:
>  * args->size handling fixes.
>  * Update context image from GGTT.
>  * Postpone context image update to pinning.
>  * Use i915_gem_active_raw instead of last_request_on_engine.
> 
> v14:
>  * Add activity tracker on intel_context to fix the lifetime issues
>    and simplify the code. (Chris Wilson)
> 
> v15:
>  * Fix context pin leak if no space in ring by simplifying the
>    context pinning sequence.
> 
> v16:
>  * Rebase for context get/set param locking changes.
>  * Just -ENODEV on !Gen11. (Joonas)
> 
> v17:
>  * Fix one Gen11 subslice enablement rule.
>  * Handle error from i915_sw_fence_await_sw_fence_gfp. (Chris Wilson)
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100899
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=107634
> Issue: https://github.com/intel/media-driver/issues/267
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin at intel.com>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin at intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Cc: Zhipeng Gong <zhipeng.gong at intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen at linux.intel.com>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk> # v15
Reviewed-by: Chris Wilson <chris at chris-wilson.co.uk>
-Chris