Re: [Intel-gfx] [PATCH 11/19] drm/i915: Update the helper to set correct mapping

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

On 15/04/2021 10:23, Matthew Auld wrote:
> On Thu, 15 Apr 2021 at 09:21, Tvrtko Ursulin
> <tvrtko.ursulin@linux.intel.com> wrote:
>>
>>
>> On 14/04/2021 17:20, Matthew Auld wrote:
>>> On Wed, 14 Apr 2021 at 16:22, Tvrtko Ursulin
>>> <tvrtko.ursulin@linux.intel.com> wrote:
>>>>
>>>>
>>>> On 12/04/2021 10:05, Matthew Auld wrote:
>>>>> From: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
>>>>>
>>>>> Determine the possible coherent map type based on object location,
>>>>> and if target has llc or if user requires an always coherent
>>>>> mapping.
>>>>>
>>>>> Cc: Matthew Auld <matthew.auld@intel.com>
>>>>> Cc: CQ Tang <cq.tang@intel.com>
>>>>> Suggested-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
>>>>> Signed-off-by: Venkata Sandeep Dhanalakota <venkata.s.dhanalakota@intel.com>
>>>>> ---
>>>>>     drivers/gpu/drm/i915/gt/intel_engine_cs.c    |  3 ++-
>>>>>     drivers/gpu/drm/i915/gt/intel_engine_pm.c    |  2 +-
>>>>>     drivers/gpu/drm/i915/gt/intel_lrc.c          |  4 +++-
>>>>>     drivers/gpu/drm/i915/gt/intel_ring.c         |  9 ++++++---
>>>>>     drivers/gpu/drm/i915/gt/selftest_context.c   |  3 ++-
>>>>>     drivers/gpu/drm/i915/gt/selftest_hangcheck.c |  4 ++--
>>>>>     drivers/gpu/drm/i915/gt/selftest_lrc.c       |  4 +++-
>>>>>     drivers/gpu/drm/i915/gt/uc/intel_guc.c       |  4 +++-
>>>>>     drivers/gpu/drm/i915/gt/uc/intel_huc.c       |  4 +++-
>>>>>     drivers/gpu/drm/i915/i915_drv.h              | 11 +++++++++--
>>>>>     drivers/gpu/drm/i915/selftests/igt_spinner.c |  4 ++--
>>>>>     11 files changed, 36 insertions(+), 16 deletions(-)
>>>>>
>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_cs.c b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
>>>>> index efe935f80c1a..b79568d370f5 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/intel_engine_cs.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_cs.c
>>>>> @@ -664,7 +664,8 @@ static int init_status_page(struct intel_engine_cs *engine)
>>>>>         if (ret)
>>>>>                 goto err;
>>>>>
>>>>> -     vaddr = i915_gem_object_pin_map(obj, I915_MAP_WB);
>>>>> +     vaddr = i915_gem_object_pin_map(obj,
>>>>> +                                     i915_coherent_map_type(engine->i915, obj, true));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 ret = PTR_ERR(vaddr);
>>>>>                 goto err_unpin;
>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_engine_pm.c b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>>>>> index 7c9af86fdb1e..47f4397095e5 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_engine_pm.c
>>>>> @@ -23,7 +23,7 @@ static void dbg_poison_ce(struct intel_context *ce)
>>>>>
>>>>>         if (ce->state) {
>>>>>                 struct drm_i915_gem_object *obj = ce->state->obj;
>>>>> -             int type = i915_coherent_map_type(ce->engine->i915);
>>>>> +             int type = i915_coherent_map_type(ce->engine->i915, obj, true);
>>>>>                 void *map;
>>>>>
>>>>>                 if (!i915_gem_object_trylock(obj))
>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>> index e86897cde984..aafe2a4df496 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
>>>>> @@ -903,7 +903,9 @@ lrc_pre_pin(struct intel_context *ce,
>>>>>         GEM_BUG_ON(!i915_vma_is_pinned(ce->state));
>>>>>
>>>>>         *vaddr = i915_gem_object_pin_map(ce->state->obj,
>>>>> -                                      i915_coherent_map_type(ce->engine->i915) |
>>>>> +                                      i915_coherent_map_type(ce->engine->i915,
>>>>> +                                                             ce->state->obj,
>>>>> +                                                             false) |
>>>>>                                          I915_MAP_OVERRIDE);
>>>>>
>>>>>         return PTR_ERR_OR_ZERO(*vaddr);
>>>>> diff --git a/drivers/gpu/drm/i915/gt/intel_ring.c b/drivers/gpu/drm/i915/gt/intel_ring.c
>>>>> index aee0a77c77e0..3cf6c7e68108 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/intel_ring.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/intel_ring.c
>>>>> @@ -53,9 +53,12 @@ int intel_ring_pin(struct intel_ring *ring, struct i915_gem_ww_ctx *ww)
>>>>>
>>>>>         if (i915_vma_is_map_and_fenceable(vma))
>>>>>                 addr = (void __force *)i915_vma_pin_iomap(vma);
>>>>> -     else
>>>>> -             addr = i915_gem_object_pin_map(vma->obj,
>>>>> -                                            i915_coherent_map_type(vma->vm->i915));
>>>>> +     else {
>>>>> +             int type = i915_coherent_map_type(vma->vm->i915, vma->obj, false);
>>>>> +
>>>>> +             addr = i915_gem_object_pin_map(vma->obj, type);
>>>>> +     }
>>>>> +
>>>>>         if (IS_ERR(addr)) {
>>>>>                 ret = PTR_ERR(addr);
>>>>>                 goto err_ring;
>>>>> diff --git a/drivers/gpu/drm/i915/gt/selftest_context.c b/drivers/gpu/drm/i915/gt/selftest_context.c
>>>>> index b9bdd1d23243..26685b927169 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/selftest_context.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/selftest_context.c
>>>>> @@ -88,7 +88,8 @@ static int __live_context_size(struct intel_engine_cs *engine)
>>>>>                 goto err;
>>>>>
>>>>>         vaddr = i915_gem_object_pin_map_unlocked(ce->state->obj,
>>>>> -                                              i915_coherent_map_type(engine->i915));
>>>>> +                                              i915_coherent_map_type(engine->i915,
>>>>> +                                                                     ce->state->obj, false));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 err = PTR_ERR(vaddr);
>>>>>                 intel_context_unpin(ce);
>>>>> diff --git a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
>>>>> index 746985971c3a..5b63d4df8c93 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/selftest_hangcheck.c
>>>>> @@ -69,7 +69,7 @@ static int hang_init(struct hang *h, struct intel_gt *gt)
>>>>>         h->seqno = memset(vaddr, 0xff, PAGE_SIZE);
>>>>>
>>>>>         vaddr = i915_gem_object_pin_map_unlocked(h->obj,
>>>>> -                                              i915_coherent_map_type(gt->i915));
>>>>> +                                              i915_coherent_map_type(gt->i915, h->obj, false));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 err = PTR_ERR(vaddr);
>>>>>                 goto err_unpin_hws;
>>>>> @@ -130,7 +130,7 @@ hang_create_request(struct hang *h, struct intel_engine_cs *engine)
>>>>>                 return ERR_CAST(obj);
>>>>>         }
>>>>>
>>>>> -     vaddr = i915_gem_object_pin_map_unlocked(obj, i915_coherent_map_type(gt->i915));
>>>>> +     vaddr = i915_gem_object_pin_map_unlocked(obj, i915_coherent_map_type(gt->i915, obj, false));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 i915_gem_object_put(obj);
>>>>>                 i915_vm_put(vm);
>>>>> diff --git a/drivers/gpu/drm/i915/gt/selftest_lrc.c b/drivers/gpu/drm/i915/gt/selftest_lrc.c
>>>>> index 85e7df6a5123..d8f6623524e8 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/selftest_lrc.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/selftest_lrc.c
>>>>> @@ -1221,7 +1221,9 @@ static int compare_isolation(struct intel_engine_cs *engine,
>>>>>         }
>>>>>
>>>>>         lrc = i915_gem_object_pin_map_unlocked(ce->state->obj,
>>>>> -                                   i915_coherent_map_type(engine->i915));
>>>>> +                                            i915_coherent_map_type(engine->i915,
>>>>> +                                                                   ce->state->obj,
>>>>> +                                                                   false));
>>>>>         if (IS_ERR(lrc)) {
>>>>>                 err = PTR_ERR(lrc);
>>>>>                 goto err_B1;
>>>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc.c b/drivers/gpu/drm/i915/gt/uc/intel_guc.c
>>>>> index 78305b2ec89d..adae04c47aab 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc.c
>>>>> @@ -682,7 +682,9 @@ int intel_guc_allocate_and_map_vma(struct intel_guc *guc, u32 size,
>>>>>         if (IS_ERR(vma))
>>>>>                 return PTR_ERR(vma);
>>>>>
>>>>> -     vaddr = i915_gem_object_pin_map_unlocked(vma->obj, I915_MAP_WB);
>>>>> +     vaddr = i915_gem_object_pin_map_unlocked(vma->obj,
>>>>> +                                              i915_coherent_map_type(guc_to_gt(guc)->i915,
>>>>> +                                                                     vma->obj, true));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 i915_vma_unpin_and_release(&vma, 0);
>>>>>                 return PTR_ERR(vaddr);
>>>>> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_huc.c b/drivers/gpu/drm/i915/gt/uc/intel_huc.c
>>>>> index 2126dd81ac38..56d2144dc6a0 100644
>>>>> --- a/drivers/gpu/drm/i915/gt/uc/intel_huc.c
>>>>> +++ b/drivers/gpu/drm/i915/gt/uc/intel_huc.c
>>>>> @@ -82,7 +82,9 @@ static int intel_huc_rsa_data_create(struct intel_huc *huc)
>>>>>         if (IS_ERR(vma))
>>>>>                 return PTR_ERR(vma);
>>>>>
>>>>> -     vaddr = i915_gem_object_pin_map_unlocked(vma->obj, I915_MAP_WB);
>>>>> +     vaddr = i915_gem_object_pin_map_unlocked(vma->obj,
>>>>> +                                              i915_coherent_map_type(gt->i915,
>>>>> +                                                                     vma->obj, true));
>>>>>         if (IS_ERR(vaddr)) {
>>>>>                 i915_vma_unpin_and_release(&vma, 0);
>>>>>                 return PTR_ERR(vaddr);
>>>>> diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
>>>>> index 69e43bf91a15..2abbc06712a4 100644
>>>>> --- a/drivers/gpu/drm/i915/i915_drv.h
>>>>> +++ b/drivers/gpu/drm/i915/i915_drv.h
>>>>> @@ -78,6 +78,7 @@
>>>>>     #include "gem/i915_gem_context_types.h"
>>>>>     #include "gem/i915_gem_shrinker.h"
>>>>>     #include "gem/i915_gem_stolen.h"
>>>>> +#include "gem/i915_gem_lmem.h"
>>>>>
>>>>>     #include "gt/intel_engine.h"
>>>>>     #include "gt/intel_gt_types.h"
>>>>> @@ -1921,9 +1922,15 @@ static inline int intel_hws_csb_write_index(struct drm_i915_private *i915)
>>>>>     }
>>>>>
>>>>>     static inline enum i915_map_type
>>>>> -i915_coherent_map_type(struct drm_i915_private *i915)
>>>>> +i915_coherent_map_type(struct drm_i915_private *i915,
>>>>> +                    struct drm_i915_gem_object *obj, bool always_coherent)
>>>>>     {
>>>>> -     return HAS_LLC(i915) ? I915_MAP_WB : I915_MAP_WC;
>>>>> +     if (i915_gem_object_is_lmem(obj))
>>>>> +             return I915_MAP_WC;
>>>>> +     if (HAS_LLC(i915) || always_coherent)
>>>>> +             return I915_MAP_WB;
>>>>> +     else
>>>>> +             return I915_MAP_WC;
>>>>
>>>> Seems this patch is doing two things.
>>>>
>>>> First it is adding lmem support to this helper by always returning WC
>>>> for lmem objects.
>>>>
>>>> Secondly it is introducing an idea of "always coherent" in a helper
>>>> called i915_coherent_map_type. Could someone explain what is coherent vs
>>>> always coherent?
>>>>
>>>> And also, why is always coherent happy with WB? Sounds counter intuitive
>>>> to me.
>>>
>>> All this does is try to keep the existing behaviour intact, whilst
>>> also ensuring that all lmem objects are mapped using only WC, no
>>> matter what. The always_coherent=true thing is for the existing places
>>> where we sometimes map the object using WB, without first considering
>>> whether the device has the fast shared LLC vs snooping. Yes, it's
>>> slightly ugly :)
>>
>> Not fully following - if we had to write kerneldoc for always_coherent
>> input argument - what it would say?
> 
> @always_coherent - If true we should always try to map the object
> using WB. If false we should only map as WB if the device supports the
> fast shared LLC, in the case of snooped devices we will map use WC.
> Note that If the resource is lmem then we will always map as WC,
> regardless of the value of always_coherent, since that's all we
> currently support.
> 
> Maybe the naming is poor?

Maybe just confusing to me, not sure yet.

So always_coherent is not about how the callers wants to use it, but 
about platform knowledge? Or a performance concern for LLC vs snooping 
cases? Does WB works (coherently) on snooping platforms?

Regards,

Tvrtko
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