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

[Matthew Auld <matthew.auld@xxxxxxxxx>]

On 19/04/2021 16:01, Tvrtko Ursulin wrote:
> On 19/04/2021 15:37, Matthew Auld wrote:
> > On 19/04/2021 15:07, Tvrtko Ursulin wrote:
> > > On 19/04/2021 12:30, Matthew Auld wrote:
> > > > On 15/04/2021 12:05, Tvrtko Ursulin wrote:
> > > > > On 15/04/2021 10:23, Matthew Auld wrote:
> > > > > > On Thu, 15 Apr 2021 at 09:21, Tvrtko Ursulin
> > > > > > <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> > > > > > > On 14/04/2021 17:20, Matthew Auld wrote:
> > > > > > > > On Wed, 14 Apr 2021 at 16:22, Tvrtko Ursulin
> > > > > > > > <tvrtko.ursulin@xxxxxxxxxxxxxxx> wrote:
> > > > > > > > > On 12/04/2021 10:05, Matthew Auld wrote:
> > > > > > > > > > From: Venkata Sandeep Dhanalakota 
> > > > > > > > > > <venkata.s.dhanalakota@xxxxxxxxx>
> > > > > > > > > >
> > > > > > > > > > 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@xxxxxxxxx>
> > > > > > > > > > Cc: CQ Tang <cq.tang@xxxxxxxxx>
> > > > > > > > > > Suggested-by: Michal Wajdeczko <michal.wajdeczko@xxxxxxxxx>
> > > > > > > > > > Signed-off-by: Venkata Sandeep Dhanalakota 
> > > > > > > > > > <venkata.s.dhanalakota@xxxxxxxxx>
> > > > > > > > > > ---
> > > > > > > > > >     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?
> > > >
> > > > The always_coherent=true is for the existing callers that want WB, 
> > > > regardless of LLC vs snooping.
> > > >
> > > > The other callers use the existing i915_coherent_map_type() which 
> > > > only gives out WB for LLC platforms.
> > > >
> > > > AFAIK, LLC vs snooping should offer the same in terms of coherency, 
> > > > but in terms of performance the shared LLC is much faster, and so 
> > > > for snooping platforms we choose to not enable WB everywhere.
> > > >
> > > > On top of that we now have lmem, but for that we only allow WC. This 
> > > > patch just rolls all of that into one helper, while keeping the 
> > > > existing behaviour unchanged.
> > >
> > > Thanks. But I am still struggling with the API. :(
> > >
> > > Is the introduction of always_coherent flag in the context of DG1 
> > > required even? AFAICT for lmem objects the flag is ignored so no?
> >
> > If we drop the flag/helper thing, then we need something like:
> >
> > type = WB;
> > if (i915_gem_object_is_lmem(obj))
> >      type = WC;
> >
> > vaddr = i915_gem_object_pin_map(obj, type);
> >
> > In all the places where we currently do:
> >
> > vaddr = i915_gem_object_pin_map(obj, WB);
> >
> > Where obj can be lmem, so ctx, ring, guc etc. Is that better or worse? 
> > The existing i915_coherent_map_type() callers should work as-is, since 
> > DG1 is snooped. And this patch just extends that to cover all cases.
> >
> > Perhaps we need a new helper instead? Maybe you have a better idea?
>
> Not yet. Would it make sense to put something in kerneldoc about when 
> callers might choose always_coherent true vs false? In terms of expected 
> usage (frequency, simplicity?) and any rules with regards when callers 
> need to worry about flushing/ordering when there are mixed read and writes?

Hmmm, looking at this again, maybe for now we should just go with:

type = WB;
if (i915_gem_object_is_lmem(obj))
      type = WC;

vaddr = i915_gem_object_pin_map(obj, type)

Which is way less confusing, plus there are only a handful of places 
where we need this, so doesn't seem too bad?

Alternatively, we could wrap that in something like:

/* Returns WB for system memory, or WC for local memory */
void *i915_gem_object_pin_map_default(obj);

Thoughts?

> Regards,
>
> Tvrtko
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