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

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 08/01/2019 14:22, Joonas Lahtinen wrote:
> 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(...).

The value is not used elsewhere so I presume you mean for readability? like:

if (IS_GEN(i915, 11) && slices == 1) {
	u8 max_subslices = min_t(u8, 4, hweight8(sseu->subslice_mask[0]) / 2);

	if (subslices > max_subslices) {
		GEM_BUG_ON(subslices & 1);
		subslice_pg = false;
		slices *= 2;
	}
}

?

I am not too bothered with one vs the other so depends how strong you 
suggest.

>> +++ 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.
>   */

At first I thought a good idea but on second thought do we want to put 
such implementation details into uapi headers? Second note maybe, but 
first I have a feeling is best left out since headers and kernel are not 
strictly tied up in deployment. Don't know, third opinion from Chris?

Regards,

Tvrtko

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