Quoting Tvrtko Ursulin (2018-09-17 12:30:57)
> From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
>
> 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@xxxxxxxxxxxxxxxxxx>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@xxxxxxxxx>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@xxxxxxxxx>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Cc: Zhipeng Gong <zhipeng.gong@xxxxxxxxx>
> Cc: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
> Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> # v15
Reviewed-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
-Chris
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