Re: [PATCH 8/8] drm/i915: Expose RPCS (SSEU) configuration to userspace

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

Quoting Lionel Landwerlin (2018-04-25 14:45:21)
> From: Chris Wilson <chris@chris-wilson.co.uk>
> 
> 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.

This hit a dead end last time due to the system wide policy needed to
avoid two parties fighting over the slice count (and going back and
forth between two slice counts would counter the benefits received from
this).

Do we now have a solution for the contention? I don't see code to
negotiate a global value, just raw setter.

Regards, Joonas

> 
> 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 = { .flags = I915_EXEC_RENDER };
> 
>         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)
> 
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100899
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
> c: 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>
> ---
>  drivers/gpu/drm/i915/i915_gem_context.c | 82 ++++++++++++++++++++++++-
>  drivers/gpu/drm/i915/intel_lrc.c        | 55 +++++++++++++++++
>  drivers/gpu/drm/i915/intel_lrc.h        |  4 ++
>  include/uapi/drm/i915_drm.h             | 28 +++++++++
>  4 files changed, 168 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
> index bdf050beeb94..b97ddcf47514 100644
> --- a/drivers/gpu/drm/i915/i915_gem_context.c
> +++ b/drivers/gpu/drm/i915/i915_gem_context.c
> @@ -740,6 +740,26 @@ int i915_gem_context_destroy_ioctl(struct drm_device *dev, void *data,
>         return 0;
>  }
>  
> +static struct i915_gem_context_sseu
> +i915_gem_context_sseu_from_user_sseu(const struct sseu_dev_info *sseu,
> +                                    const struct drm_i915_gem_context_param_sseu *user_sseu)
> +{
> +       struct i915_gem_context_sseu value = {
> +               .slice_mask = user_sseu->packed.slice_mask == 0 ?
> +                             sseu->slice_mask :
> +                             (user_sseu->packed.slice_mask & sseu->slice_mask),
> +               .subslice_mask = user_sseu->packed.subslice_mask == 0 ?
> +                                sseu->subslice_mask[0] :
> +                                (user_sseu->packed.subslice_mask & sseu->subslice_mask[0]),
> +               .min_eus_per_subslice = min(user_sseu->packed.min_eus_per_subslice,
> +                                           sseu->max_eus_per_subslice),
> +               .max_eus_per_subslice = min(user_sseu->packed.max_eus_per_subslice,
> +                                           sseu->max_eus_per_subslice),
> +       };
> +
> +       return value;
> +}
> +
>  int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
>                                     struct drm_file *file)
>  {
> @@ -777,6 +797,37 @@ int i915_gem_context_getparam_ioctl(struct drm_device *dev, void *data,
>         case I915_CONTEXT_PARAM_PRIORITY:
>                 args->value = ctx->sched.priority;
>                 break;
> +       case I915_CONTEXT_PARAM_SSEU: {
> +               struct drm_i915_gem_context_param_sseu param_sseu;
> +               struct intel_engine_cs *engine;
> +
> +               if (copy_from_user(&param_sseu, u64_to_user_ptr(args->value),
> +                                  sizeof(param_sseu))) {
> +                       ret = -EFAULT;
> +                       break;
> +               }
> +
> +               engine = i915_gem_engine_from_flags(to_i915(dev), file,
> +                                                   param_sseu.flags);
> +               if (!engine) {
> +                       ret = -EINVAL;
> +                       break;
> +               }
> +
> +               param_sseu.packed.slice_mask =
> +                       ctx->engine[engine->id].sseu.slice_mask;
> +               param_sseu.packed.subslice_mask =
> +                       ctx->engine[engine->id].sseu.subslice_mask;
> +               param_sseu.packed.min_eus_per_subslice =
> +                       ctx->engine[engine->id].sseu.min_eus_per_subslice;
> +               param_sseu.packed.max_eus_per_subslice =
> +                       ctx->engine[engine->id].sseu.max_eus_per_subslice;
> +
> +               if (copy_to_user(u64_to_user_ptr(args->value), &param_sseu,
> +                                sizeof(param_sseu)))
> +                       ret = -EFAULT;
> +               break;
> +       }
>         default:
>                 ret = -EINVAL;
>                 break;
> @@ -832,7 +883,6 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
>                 else
>                         i915_gem_context_clear_bannable(ctx);
>                 break;
> -
>         case I915_CONTEXT_PARAM_PRIORITY:
>                 {
>                         s64 priority = args->value;
> @@ -851,7 +901,37 @@ int i915_gem_context_setparam_ioctl(struct drm_device *dev, void *data,
>                                 ctx->sched.priority = priority;
>                 }
>                 break;
> +       case I915_CONTEXT_PARAM_SSEU:
> +               if (args->size)
> +                       ret = -EINVAL;
> +               else if (!HAS_EXECLISTS(ctx->i915))
> +                       ret = -ENODEV;
> +               else {
> +                       struct drm_i915_private *dev_priv = to_i915(dev);
> +                       struct drm_i915_gem_context_param_sseu user_sseu;
> +                       struct i915_gem_context_sseu ctx_sseu;
> +                       struct intel_engine_cs *engine;
> +
> +                       if (copy_from_user(&user_sseu, u64_to_user_ptr(args->value),
> +                                          sizeof(user_sseu))) {
> +                               ret = -EFAULT;
> +                               break;
> +                       }
> +
> +                       engine = i915_gem_engine_from_flags(dev_priv, file,
> +                                                           user_sseu.flags);
> +                       if (!engine) {
> +                               ret = -EINVAL;
> +                               break;
> +                       }
> +
> +                       ctx_sseu =
> +                               i915_gem_context_sseu_from_user_sseu(&INTEL_INFO(dev_priv)->sseu,
> +                                                                    &user_sseu);
>  
> +                       ret = intel_lr_context_set_sseu(ctx, engine, &ctx_sseu);
> +               }
> +               break;
>         default:
>                 ret = -EINVAL;
>                 break;
> diff --git a/drivers/gpu/drm/i915/intel_lrc.c b/drivers/gpu/drm/i915/intel_lrc.c
> index dca17ef24de5..9caddcb1f234 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/intel_lrc.c
> @@ -2711,6 +2711,61 @@ void intel_lr_context_resume(struct drm_i915_private *dev_priv)
>         }
>  }
>  
> +int intel_lr_context_set_sseu(struct i915_gem_context *ctx,
> +                             struct intel_engine_cs *engine,
> +                             struct i915_gem_context_sseu *sseu)
> +{
> +       struct drm_i915_private *dev_priv = ctx->i915;
> +       struct intel_context *ce;
> +       enum intel_engine_id id;
> +       int ret;
> +
> +       lockdep_assert_held(&dev_priv->drm.struct_mutex);
> +
> +       if (memcmp(sseu, &ctx->engine[engine->id].sseu, sizeof(*sseu)) == 0)
> +               return 0;
> +
> +       /*
> +        * We can only program this on render ring.
> +        */
> +       ce = &ctx->engine[RCS];
> +
> +       if (ce->pin_count) { /* Assume that the context is active! */
> +               ret = i915_gem_switch_to_kernel_context(dev_priv);
> +               if (ret)
> +                       return ret;
> +
> +               ret = i915_gem_wait_for_idle(dev_priv,
> +                                            I915_WAIT_INTERRUPTIBLE |
> +                                            I915_WAIT_LOCKED);
> +               if (ret)
> +                       return ret;
> +       }
> +
> +       if (ce->state) {
> +               void *vaddr = i915_gem_object_pin_map(ce->state->obj, I915_MAP_WB);
> +               u32 *regs;
> +
> +               if (IS_ERR(vaddr))
> +                       return PTR_ERR(vaddr);
> +
> +               regs = vaddr + LRC_STATE_PN * PAGE_SIZE;
> +
> +               regs[CTX_R_PWR_CLK_STATE + 1] =
> +                       make_rpcs(&INTEL_INFO(dev_priv)->sseu, sseu);
> +               i915_gem_object_unpin_map(ce->state->obj);
> +       }
> +
> +       /*
> +        * Apply the configuration to all engine. Our hardware doesn't
> +        * currently support different configurations for each engine.
> +        */
> +       for_each_engine(engine, dev_priv, id)
> +               ctx->engine[id].sseu = *sseu;
> +
> +       return 0;
> +}
> +
>  #if IS_ENABLED(CONFIG_DRM_I915_SELFTEST)
>  #include "selftests/intel_lrc.c"
>  #endif
> diff --git a/drivers/gpu/drm/i915/intel_lrc.h b/drivers/gpu/drm/i915/intel_lrc.h
> index d91d69a17206..4c84266814fa 100644
> --- a/drivers/gpu/drm/i915/intel_lrc.h
> +++ b/drivers/gpu/drm/i915/intel_lrc.h
> @@ -112,4 +112,8 @@ intel_lr_context_descriptor(struct i915_gem_context *ctx,
>         return ctx->engine[engine->id].lrc_desc;
>  }
>  
> +int intel_lr_context_set_sseu(struct i915_gem_context *ctx,
> +                             struct intel_engine_cs *engine,
> +                             struct i915_gem_context_sseu *sseu);
> +
>  #endif /* _INTEL_LRC_H_ */
> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
> index 96eda8176030..75749ce11c03 100644
> --- a/include/uapi/drm/i915_drm.h
> +++ b/include/uapi/drm/i915_drm.h
> @@ -1456,9 +1456,37 @@ 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;
>  };
>  
> +struct drm_i915_gem_context_param_sseu {
> +       /*
> +        * Engine to be configured or queried. Same value you would use with
> +        * drm_i915_gem_execbuffer2.
> +        */
> +       __u64 flags;
> +
> +       /*
> +        * Setting slice_mask or subslice_mask to 0 will make the context use
> +        * masks reported respectively by I915_PARAM_SLICE_MASK or
> +        * I915_PARAM_SUBSLICE_MASK.
> +        */
> +       union {
> +               struct {
> +                       __u8 slice_mask;
> +                       __u8 subslice_mask;
> +                       __u8 min_eus_per_subslice;
> +                       __u8 max_eus_per_subslice;
> +               } packed;
> +               __u64 value;
> +       };
> +};
> +
>  enum drm_i915_oa_format {
>         I915_OA_FORMAT_A13 = 1,     /* HSW only */
>         I915_OA_FORMAT_A29,         /* HSW only */
> -- 
> 2.17.0
> 
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