Re: [PATCH 5/7] drm/i915: Expose RPCS (SSEU) configuration to userspace (Gen11 only)

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

Quoting Tvrtko Ursulin (2019-01-08 13:22:50)
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> We want to allow userspace to reconfigure the subslice configuration on a
> per context basis.
> 
> This is required for the functional requirement of shutting down non-VME
> enabled sub-slices on Gen11 parts.
> 
> 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 or whilst idle, the adjustment
> is for "free"; otherwise if the context is active we queue a request to do
> so (using the kernel context), following all other activity by that
> context, which is also marked as barrier for all following submission
> against the same context.
> 
> Since the overhead of device re-configuration during context switching can
> be significant, especially in multi-context workloads, we limit this new
> uAPI to only support the Gen11 VME use case. In this use case either the
> device is fully enabled, and exactly one slice and half of the subslices
> are enabled.
> 
> Example usage:
> 
>         struct drm_i915_gem_context_param_sseu sseu = { };
>         struct drm_i915_gem_context_param arg =
>                 { .param = I915_CONTEXT_PARAM_SSEU,
>                   .ctx_id = gem_context_create(fd),
>                   .size = sizeof(sseu),
>                   .value = to_user_pointer(&sseu)
>                 };
> 
>         /* Query device defaults. */
>         gem_context_get_param(fd, &arg);
> 
>         /* Set VME configuration on a 1x6x8 part. */
>         sseu.slice_mask = 0x1;
>         sseu.subslice_mask = 0xe0;
>         gem_context_set_param(fd, &arg);
> 
> 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)
> 
> v18:
>  * Update commit message. (Joonas)
>  * Restrict uAPI to VME use case. (Joonas)
> 
> v19:
>  * Rebase.
> 
> v20:
>  * Rebase for ce->active_tracker.
> 
> v21:
>  * Rebase for IS_GEN changes.
> 
> v22:
>  * Reserve uAPI for flags straight away. (Chris Wilson)
> 
> v23:
>  * Rebase for RUNTIME_INFO.
> 
> 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@chris-wilson.co.uk>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> Cc: Dmitry Rogozhkin <dmitry.v.rogozhkin@intel.com>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Zhipeng Gong <zhipeng.gong@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk> # v21

<SNIP>

> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2377,7 +2377,9 @@ u32 gen8_make_rpcs(struct drm_i915_private *i915, struct intel_sseu *req_sseu)
>          * subslices are enabled, or a count between one and four on the first
>          * slice.
>          */
> -       if (IS_GEN(i915, 11) && slices == 1 && subslices >= 4) {
> +       if (IS_GEN(i915, 11) &&
> +           slices == 1 &&
> +           subslices > min_t(u8, 4, hweight8(sseu->subslice_mask[0]) / 2)) {

Could use it's own variable max_subslices = min_t(...).

> +++ b/include/uapi/drm/i915_drm.h
> @@ -1486,9 +1486,52 @@ struct drm_i915_gem_context_param {
>  #define   I915_CONTEXT_MAX_USER_PRIORITY       1023 /* inclusive */
>  #define   I915_CONTEXT_DEFAULT_PRIORITY                0
>  #define   I915_CONTEXT_MIN_USER_PRIORITY       -1023 /* inclusive */
> +       /*
> +        * When using the following param, value should be a pointer to
> +        * drm_i915_gem_context_param_sseu.
> +        */
> +#define I915_CONTEXT_PARAM_SSEU                0x7
>         __u64 value;
>  };

Maybe we should amend some comments?

/*
 * NOTE: Can currently only be used to switch between VME enabled
 *       slice configuration vs. full on Icelake (Gen11)
 *
 * NOTE: Slice configuration requests are ignored when perf is enabled.
 */

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
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