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

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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? 

Regards,

Tvrtko
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