[Intel-gfx] [PATCH v15 1/1] drm/i915: Allow user to set cache at BO creation
Yang, Fei
fei.yang at intel.com
Tue Jun 6 06:51:06 UTC 2023
>> On 31/05/2023 18:10, fei.yang at intel.com wrote:
>>> From: Fei Yang <fei.yang at intel.com>
>>>
>>> To comply with the design that buffer objects shall have immutable
>>> cache setting through out their life cycle, {set, get}_caching ioctl's
>>> are no longer supported from MTL onward. With that change caching
>>> policy can only be set at object creation time. The current code
>>> applies a default (platform dependent) cache setting for all objects.
>>> However this is not optimal for performance tuning. The patch extends
>>> the existing gem_create uAPI to let user set PAT index for the object
>>> at creation time.
>>> The new extension is platform independent, so UMD's can switch to using
>>> this extension for older platforms as well, while {set, get}_caching are
>>> still supported on these legacy paltforms for compatibility reason.
>>>
>>> Note: The detailed description of PAT index is missing in current PRM
>>> even for older hardware and will be added by the next PRM update under
>>> chapter name "Memory Views".
>>>
>>> BSpec: 45101
>>>
>>> Mesa support has been submitted in this merge request:
>>> https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/22878
>>>
>>> The media driver is supported by the following commits:
>>> https://github.com/intel/media-driver/commit/92c00a857433ebb34ec575e9834f473c6fcb6341
>>> https://github.com/intel/media-driver/commit/fd375cf2c5e1f6bf6b43258ff797b3134aadc9fd
>>> https://github.com/intel/media-driver/commit/08dd244b22484770a33464c2c8ae85430e548000
>>
>> On which platforms will media-driver use the uapi? I couldn't easily
>> figure out myself from the links above and also in the master branch I
>> couldn't find the implementation of CachePolicyGetPATIndex.
>
> These commits look like platform independent. Carl, could you chime in here?
Confirmed with Carl and Lihao offline that the media driver is calling set_pat
extension in common code path, so the use of set_pat extension is platform
independent. The only problem right now is that the gmm library is not returning
correct PAT index for all hardware platforms, so on some platforms the call would
be bypassed and fall back to the old way.
I think this is the correct implementation. It should be platform independent as
long as the application knows what PAT index to set. Updating the gmm library to
understand PAT index for each hardware platform is a separate issue.
>> Now that PRMs for Tigerlake have been published and Meteorlake situation
>> is documented indirectly in Mesa code, my only remaining concern is with
>> the older platforms. So if there is no particular reason to have the
>> extension working on those, I would strongly suggest we disable there.
>
> What's the concern? There is no change required for older platforms, existing
> user space code should continue to work. And this extension should be made
> available for any new development because the cache settings for BO's need
> to be immutable. And that is platform independent.
>
>> For a precedent see I915_CONTEXT_PARAM_SSEU and how it allows the
>> extension only on Gen11 and only for a very specific usecase (see
>> restrictions in set_sseu() and i915_gem_user_to_context_sseu()).
>>
>> Regards,
>>
>> Tvrtko
>>
>>>
>>> The IGT test related to this change is
>>> igt at gem_create@create-ext-set-pat
>>>
>>> Signed-off-by: Fei Yang <fei.yang at intel.com>
>>> Cc: Chris Wilson <chris.p.wilson at linux.intel.com>
>>> Cc: Matt Roper <matthew.d.roper at intel.com>
>>> Cc: Andi Shyti <andi.shyti at linux.intel.com>
>>> Reviewed-by: Andi Shyti <andi.shyti at linux.intel.com>
>>> Acked-by: Jordan Justen <jordan.l.justen at intel.com>
>>> Tested-by: Jordan Justen <jordan.l.justen at intel.com>
>>> Acked-by: Carl Zhang <carl.zhang at intel.com>
>>> Tested-by: Lihao Gu <lihao.gu at intel.com>
>>> ---
>>> drivers/gpu/drm/i915/gem/i915_gem_create.c | 36 +++++++++++++++++++
>>> drivers/gpu/drm/i915/gem/i915_gem_object.c | 6 ++++
>>> include/uapi/drm/i915_drm.h | 41 ++++++++++++++++++++++
>>> 3 files changed, 83 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_create.c b/drivers/gpu/drm/i915/gem/i915_gem_create.c
>>> index bfe1dbda4cb7..644a936248ad 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_create.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_create.c
>>> @@ -245,6 +245,7 @@ struct create_ext {
>>> unsigned int n_placements;
>>> unsigned int placement_mask;
>>> unsigned long flags;
>>> + unsigned int pat_index;
>>> };
>>>
>>> static void repr_placements(char *buf, size_t size,
>>> @@ -394,11 +395,39 @@ static int ext_set_protected(struct i915_user_extension __user *base, void *data
>>> return 0;
>>> }
>>>
>>> +static int ext_set_pat(struct i915_user_extension __user *base, void *data)
>>> +{
>>> + struct create_ext *ext_data = data;
>>> + struct drm_i915_private *i915 = ext_data->i915;
>>> + struct drm_i915_gem_create_ext_set_pat ext;
>>> + unsigned int max_pat_index;
>>> +
>>> + BUILD_BUG_ON(sizeof(struct drm_i915_gem_create_ext_set_pat) !=
>>> + offsetofend(struct drm_i915_gem_create_ext_set_pat, rsvd));
>>> +
>>> + if (copy_from_user(&ext, base, sizeof(ext)))
>>> + return -EFAULT;
>>> +
>>> + max_pat_index = INTEL_INFO(i915)->max_pat_index;
>>> +
>>> + if (ext.pat_index > max_pat_index) {
>>> + drm_dbg(&i915->drm, "PAT index is invalid: %u\n",
>>> + ext.pat_index);
>>> + return -EINVAL;
>>> + }
>>> +
>>> + ext_data->pat_index = ext.pat_index;
>>> +
>>> + return 0;
>>> +}
>>> +
>>> static const i915_user_extension_fn create_extensions[] = {
>>> [I915_GEM_CREATE_EXT_MEMORY_REGIONS] = ext_set_placements,
>>> [I915_GEM_CREATE_EXT_PROTECTED_CONTENT] = ext_set_protected,
>>> + [I915_GEM_CREATE_EXT_SET_PAT] = ext_set_pat,
>>> };
>>>
>>> +#define PAT_INDEX_NOT_SET 0xffff
>>> /**
>>> * i915_gem_create_ext_ioctl - Creates a new mm object and returns a handle to it.
>>> * @dev: drm device pointer
>>> @@ -418,6 +447,7 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>>> if (args->flags & ~I915_GEM_CREATE_EXT_FLAG_NEEDS_CPU_ACCESS)
>>> return -EINVAL;
>>>
>>> + ext_data.pat_index = PAT_INDEX_NOT_SET;
>>> ret = i915_user_extensions(u64_to_user_ptr(args->extensions),
>>> create_extensions,
>>> ARRAY_SIZE(create_extensions),
>>> @@ -454,5 +484,11 @@ i915_gem_create_ext_ioctl(struct drm_device *dev, void *data,
>>> if (IS_ERR(obj))
>>> return PTR_ERR(obj);
>>>
>>> + if (ext_data.pat_index != PAT_INDEX_NOT_SET) {
>>> + i915_gem_object_set_pat_index(obj, ext_data.pat_index);
>>> + /* Mark pat_index is set by UMD */
>>> + obj->pat_set_by_user = true;
>>> + }
>>> +
>>> return i915_gem_publish(obj, file, &args->size, &args->handle);
>>> }
>>> diff --git a/drivers/gpu/drm/i915/gem/i915_gem_object.c b/drivers/gpu/drm/i915/gem/i915_gem_object.c
>>> index 46a19b099ec8..97ac6fb37958 100644
>>> --- a/drivers/gpu/drm/i915/gem/i915_gem_object.c
>>> +++ b/drivers/gpu/drm/i915/gem/i915_gem_object.c
>>> @@ -208,6 +208,12 @@ bool i915_gem_object_can_bypass_llc(struct drm_i915_gem_object *obj)
>>> if (!(obj->flags & I915_BO_ALLOC_USER))
>>> return false;
>>>
>>> + /*
>>> + * Always flush cache for UMD objects at creation time.
>>> + */
>>> + if (obj->pat_set_by_user)
>>> + return true;
>>> +
>>> /*
>>> * EHL and JSL add the 'Bypass LLC' MOCS entry, which should make it
>>> * possible for userspace to bypass the GTT caching bits set by the
>>> diff --git a/include/uapi/drm/i915_drm.h b/include/uapi/drm/i915_drm.h
>>> index f31dfacde601..4083a23e0614 100644
>>> --- a/include/uapi/drm/i915_drm.h
>>> +++ b/include/uapi/drm/i915_drm.h
>>> @@ -3679,9 +3679,13 @@ struct drm_i915_gem_create_ext {
>>> *
>>> * For I915_GEM_CREATE_EXT_PROTECTED_CONTENT usage see
>>> * struct drm_i915_gem_create_ext_protected_content.
>>> + *
>>> + * For I915_GEM_CREATE_EXT_SET_PAT usage see
>>> + * struct drm_i915_gem_create_ext_set_pat.
>>> */
>>> #define I915_GEM_CREATE_EXT_MEMORY_REGIONS 0
>>> #define I915_GEM_CREATE_EXT_PROTECTED_CONTENT 1
>>> +#define I915_GEM_CREATE_EXT_SET_PAT 2
>>> __u64 extensions;
>>> };
>>>
>>> @@ -3796,6 +3800,43 @@ struct drm_i915_gem_create_ext_protected_content {
>>> __u32 flags;
>>> };
>>>
>>> +/**
>>> + * struct drm_i915_gem_create_ext_set_pat - The
>>> + * I915_GEM_CREATE_EXT_SET_PAT extension.
>>> + *
>>> + * If this extension is provided, the specified caching policy (PAT index) is
>>> + * applied to the buffer object.
>>> + *
>>> + * Below is an example on how to create an object with specific caching policy:
>>> + *
>>> + * .. code-block:: C
>>> + *
>>> + * struct drm_i915_gem_create_ext_set_pat set_pat_ext = {
>>> + * .base = { .name = I915_GEM_CREATE_EXT_SET_PAT },
>>> + * .pat_index = 0,
>>> + * };
>>> + * struct drm_i915_gem_create_ext create_ext = {
>>> + * .size = PAGE_SIZE,
>>> + * .extensions = (uintptr_t)&set_pat_ext,
>>> + * };
>>> + *
>>> + * int err = ioctl(fd, DRM_IOCTL_I915_GEM_CREATE_EXT, &create_ext);
>>> + * if (err) ...
>>> + */
>>> +struct drm_i915_gem_create_ext_set_pat {
>>> + /** @base: Extension link. See struct i915_user_extension. */
>>> + struct i915_user_extension base;
>>> + /**
>>> + * @pat_index: PAT index to be set
>>> + * PAT index is a bit field in Page Table Entry to control caching
>>> + * behaviors for GPU accesses. The definition of PAT index is
>>> + * platform dependent and can be found in hardware specifications,
>>> + */
>>> + __u32 pat_index;
>>> + /** @rsvd: reserved for future use */
>>> + __u32 rsvd;
>>> +};
>>> +
>>> /* ID of the protected content session managed by i915 when PXP is active */
>>> #define I915_PROTECTED_CONTENT_DEFAULT_SESSION 0xf
>>>
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