On 08/07/2019 12:19, Chris Wilson wrote:
Avoid a global idle barrier by reconfiguring each context by rewriting
them with MI_STORE_DWORD from the kernel context.

v2: We only need to determine the desired register values once, they are
the same for all contexts.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Lionel Landwerlin <lionel.g.landwer...@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwer...@intel.com>
---
  drivers/gpu/drm/i915/gem/i915_gem_context.c |   2 +
  drivers/gpu/drm/i915/gt/intel_lrc.c         |   7 +-
  drivers/gpu/drm/i915/i915_perf.c            | 248 +++++++++++++++-----
  3 files changed, 195 insertions(+), 62 deletions(-)

diff --git a/drivers/gpu/drm/i915/gem/i915_gem_context.c 
b/drivers/gpu/drm/i915/gem/i915_gem_context.c
index e367dce2a696..1f0d10bb88c1 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_context.c
@@ -624,7 +624,9 @@ i915_gem_context_create_kernel(struct drm_i915_private 
*i915, int prio)
        ctx->sched.priority = I915_USER_PRIORITY(prio);
        ctx->ring_size = PAGE_SIZE;
+ /* Isolate the kernel context from prying eyes and sticky fingers */
        GEM_BUG_ON(!i915_gem_context_is_kernel(ctx));
+       list_del_init(&ctx->link);

Why exactly?

Any repercussions for i915_sysfs/i915_l3_write? debugfs I gather you won't care about?

Should adding to i915->contexts.list be done from gem_context_register? What remains not a kernel context, but on a list?

Won't preempt context be missed in re-configuration?

Regards,

Tvrtko

return ctx;
  }
diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c 
b/drivers/gpu/drm/i915/gt/intel_lrc.c
index e1ae1399c72b..9cc5374401e1 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -1552,9 +1552,12 @@ __execlists_update_reg_state(struct intel_context *ce,
        regs[CTX_RING_TAIL + 1] = ring->tail;
/* RPCS */
-       if (engine->class == RENDER_CLASS)
+       if (engine->class == RENDER_CLASS) {
                regs[CTX_R_PWR_CLK_STATE + 1] =
                        intel_sseu_make_rpcs(engine->i915, &ce->sseu);
+
+               i915_oa_init_reg_state(engine, ce, regs);
+       }
  }
static int
@@ -2966,8 +2969,6 @@ static void execlists_init_reg_state(u32 *regs,
        if (rcs) {
                regs[CTX_LRI_HEADER_2] = MI_LOAD_REGISTER_IMM(1);
                CTX_REG(regs, CTX_R_PWR_CLK_STATE, GEN8_R_PWR_CLK_STATE, 0);
-
-               i915_oa_init_reg_state(engine, ce, regs);
        }
regs[CTX_END] = MI_BATCH_BUFFER_END;
diff --git a/drivers/gpu/drm/i915/i915_perf.c b/drivers/gpu/drm/i915/i915_perf.c
index 357e63beb373..25c34a0b521e 100644
--- a/drivers/gpu/drm/i915/i915_perf.c
+++ b/drivers/gpu/drm/i915/i915_perf.c
@@ -1630,6 +1630,27 @@ static void hsw_disable_metric_set(struct 
drm_i915_private *dev_priv)
                                      ~GT_NOA_ENABLE));
  }
+static u32 oa_config_flex_reg(const struct i915_oa_config *oa_config,
+                             i915_reg_t reg)
+{
+       u32 mmio = i915_mmio_reg_offset(reg);
+       int i;
+
+       /*
+        * This arbitrary default will select the 'EU FPU0 Pipeline
+        * Active' event. In the future it's anticipated that there
+        * will be an explicit 'No Event' we can select, but not yet...
+        */
+       if (!oa_config)
+               return 0;
+
+       for (i = 0; i < oa_config->flex_regs_len; i++) {
+               if (i915_mmio_reg_offset(oa_config->flex_regs[i].addr) == mmio)
+                       return oa_config->flex_regs[i].value;
+       }
+
+       return 0;
+}
  /*
   * NB: It must always remain pointer safe to run this even if the OA unit
   * has been disabled.
@@ -1663,28 +1684,8 @@ gen8_update_reg_state_unlocked(struct intel_context *ce,
                GEN8_OA_COUNTER_RESUME);
for (i = 0; i < ARRAY_SIZE(flex_regs); i++) {
-               u32 state_offset = ctx_flexeu0 + i * 2;
-               u32 mmio = i915_mmio_reg_offset(flex_regs[i]);
-
-               /*
-                * This arbitrary default will select the 'EU FPU0 Pipeline
-                * Active' event. In the future it's anticipated that there
-                * will be an explicit 'No Event' we can select, but not yet...
-                */
-               u32 value = 0;
-
-               if (oa_config) {
-                       u32 j;
-
-                       for (j = 0; j < oa_config->flex_regs_len; j++) {
-                               if 
(i915_mmio_reg_offset(oa_config->flex_regs[j].addr) == mmio) {
-                                       value = oa_config->flex_regs[j].value;
-                                       break;
-                               }
-                       }
-               }
-
-               CTX_REG(reg_state, state_offset, flex_regs[i], value);
+               CTX_REG(reg_state, ctx_flexeu0 + i * 2, flex_regs[i],
+                       oa_config_flex_reg(oa_config, flex_regs[i]));
        }
CTX_REG(reg_state,
@@ -1692,6 +1693,107 @@ gen8_update_reg_state_unlocked(struct intel_context *ce,
                intel_sseu_make_rpcs(i915, &ce->sseu));
  }
+struct flex {
+       i915_reg_t reg;
+       u32 offset;
+       u32 value;
+};
+
+static int
+gen8_store_flex(struct i915_request *rq,
+               struct intel_context *ce,
+               const struct flex *flex, unsigned int count)
+{
+       u32 offset;
+       u32 *cs;
+
+       cs = intel_ring_begin(rq, 4 * count);
+       if (IS_ERR(cs))
+               return PTR_ERR(cs);
+
+       offset = i915_ggtt_offset(ce->state) + LRC_STATE_PN * PAGE_SIZE;
+       do {
+               *cs++ = MI_STORE_DWORD_IMM_GEN4 | MI_USE_GGTT;
+               *cs++ = offset + (flex->offset + 1) * sizeof(u32);
+               *cs++ = 0;
+               *cs++ = flex->value;
+       } while (flex++, --count);
+
+       intel_ring_advance(rq, cs);
+
+       return 0;
+}
+
+static int
+gen8_load_flex(struct i915_request *rq,
+              struct intel_context *ce,
+              const struct flex *flex, unsigned int count)
+{
+       u32 *cs;
+
+       GEM_BUG_ON(!count || count > 63);
+
+       cs = intel_ring_begin(rq, 2 * count + 2);
+       if (IS_ERR(cs))
+               return PTR_ERR(cs);
+
+       *cs++ = MI_LOAD_REGISTER_IMM(count);
+       do {
+               *cs++ = i915_mmio_reg_offset(flex->reg);
+               *cs++ = flex->value;
+       } while (flex++, --count);
+       *cs++ = MI_NOOP;
+
+       intel_ring_advance(rq, cs);
+
+       return 0;
+}
+
+static int gen8_modify_context(struct intel_context *ce,
+                              const struct flex *flex, unsigned int count)
+{
+       struct i915_request *rq;
+       int err;
+
+       lockdep_assert_held(&ce->pin_mutex);
+
+       rq = i915_request_create(ce->engine->kernel_context);
+       if (IS_ERR(rq))
+               return PTR_ERR(rq);
+
+       /* Serialise with the remote context */
+       err = i915_active_request_set(&ce->ring->timeline->last_request, rq);
+       if (err)
+               goto out_add;
+
+       /* Keep the remote context alive until after we finish editing */
+       err = i915_active_ref(&ce->active, rq->fence.context, rq);
+       if (err)
+               goto out_add;
+
+       err = gen8_store_flex(rq, ce, flex, count);
+
+out_add:
+       i915_request_add(rq);
+       return err;
+}
+
+static int gen8_modify_self(struct intel_context *ce,
+                           const struct flex *flex, unsigned int count)
+{
+       struct i915_request *rq;
+       int err;
+
+       rq = i915_request_create(ce);
+       if (IS_ERR(rq))
+               return PTR_ERR(rq);
+
+       err = gen8_load_flex(rq, ce, flex, count);
+
+       i915_request_add(rq);
+       return err;
+}
+
  /*
   * Manages updating the per-context aspects of the OA stream
   * configuration across all contexts.
@@ -1716,15 +1818,43 @@ gen8_update_reg_state_unlocked(struct intel_context *ce,
   *
   * Note: it's only the RCS/Render context that has any OA state.
   */
-static int gen8_configure_all_contexts(struct drm_i915_private *dev_priv,
+static int gen8_configure_all_contexts(struct drm_i915_private *i915,
                                       const struct i915_oa_config *oa_config)
  {
-       unsigned int map_type = i915_coherent_map_type(dev_priv);
+       /* The MMIO offsets for Flex EU registers aren't contiguous */
+       const u32 ctx_flexeu0 = i915->perf.oa.ctx_flexeu0_offset;
+#define ctx_flexeuN(N) (ctx_flexeu0 + 2 * (N))
+       struct flex regs[] = {
+               {
+                       GEN8_R_PWR_CLK_STATE,
+                       CTX_R_PWR_CLK_STATE,
+               },
+               {
+                       GEN8_OACTXCONTROL,
+                       i915->perf.oa.ctx_oactxctrl_offset,
+                       ((i915->perf.oa.period_exponent << 
GEN8_OA_TIMER_PERIOD_SHIFT) |
+                        (i915->perf.oa.periodic ? GEN8_OA_TIMER_ENABLE : 0) |
+                        GEN8_OA_COUNTER_RESUME)
+               },
+               { EU_PERF_CNTL0, ctx_flexeuN(0) },
+               { EU_PERF_CNTL1, ctx_flexeuN(1) },
+               { EU_PERF_CNTL2, ctx_flexeuN(2) },
+               { EU_PERF_CNTL3, ctx_flexeuN(3) },
+               { EU_PERF_CNTL4, ctx_flexeuN(4) },
+               { EU_PERF_CNTL5, ctx_flexeuN(5) },
+               { EU_PERF_CNTL6, ctx_flexeuN(6) },
+       };
+#undef ctx_flexeuN
+       struct intel_engine_cs *engine;
        struct i915_gem_context *ctx;
-       struct i915_request *rq;
-       int ret;
+       enum intel_engine_id id;
+       int err;
+       int i;
+
+       for (i = 2; i < ARRAY_SIZE(regs); i++)
+               regs[i].value = oa_config_flex_reg(oa_config, regs[i].reg);
- lockdep_assert_held(&dev_priv->drm.struct_mutex);
+       lockdep_assert_held(&i915->drm.struct_mutex);
/*
         * The OA register config is setup through the context image. This image
@@ -1736,58 +1866,58 @@ static int gen8_configure_all_contexts(struct 
drm_i915_private *dev_priv,
         * this might leave small interval of time where the OA unit is
         * configured at an invalid sampling period.
         *
-        * So far the best way to work around this issue seems to be draining
-        * the GPU from any submitted work.
+        * Note that since we emit all requests from a single ring, there
+        * is still an implicit global barrier here that may cause a high
+        * priority context to wait for an otherwise independent low priority
+        * context. Contexts idle at the time of reconfiguration are not
+        * trapped behind the barrier.
         */
-       ret = i915_gem_wait_for_idle(dev_priv,
-                                    I915_WAIT_LOCKED,
-                                    MAX_SCHEDULE_TIMEOUT);
-       if (ret)
-               return ret;
-
-       /* Update all contexts now that we've stalled the submission. */
-       list_for_each_entry(ctx, &dev_priv->contexts.list, link) {
+       list_for_each_entry(ctx, &i915->contexts.list, link) {
                struct i915_gem_engines_iter it;
                struct intel_context *ce;
for_each_gem_engine(ce,
                                    i915_gem_context_lock_engines(ctx),
                                    it) {
-                       u32 *regs;
-
                        if (ce->engine->class != RENDER_CLASS)
                                continue;
- /* OA settings will be set upon first use */
-                       if (!ce->state)
-                               continue;
-
-                       regs = i915_gem_object_pin_map(ce->state->obj,
-                                                      map_type);
-                       if (IS_ERR(regs)) {
-                               i915_gem_context_unlock_engines(ctx);
-                               return PTR_ERR(regs);
-                       }
+                       err = intel_context_lock_pinned(ce);
+                       if (err)
+                               break;
- ce->state->obj->mm.dirty = true;
-                       regs += LRC_STATE_PN * PAGE_SIZE / sizeof(*regs);
+                       regs[0].value = intel_sseu_make_rpcs(i915, &ce->sseu);
- gen8_update_reg_state_unlocked(ce, regs, oa_config);
+                       /* Otherwise OA settings will be set upon first use */
+                       if (intel_context_is_pinned(ce))
+                               err = gen8_modify_context(ce, regs, 
ARRAY_SIZE(regs));
- i915_gem_object_unpin_map(ce->state->obj);
+                       intel_context_unlock_pinned(ce);
+                       if (err)
+                               break;
                }
                i915_gem_context_unlock_engines(ctx);
+               if (err)
+                       return err;
        }
/*
-        * Apply the configuration by doing one context restore of the edited
-        * context image.
+        * After updating all other contexts, we need to modify ourselves.
+        * If we don't modify the kernel_context, we do not get events while
+        * idle.
         */
-       rq = i915_request_create(dev_priv->engine[RCS0]->kernel_context);
-       if (IS_ERR(rq))
-               return PTR_ERR(rq);
+       for_each_engine(engine, i915, id) {
+               struct intel_context *ce = engine->kernel_context;
- i915_request_add(rq);
+               if (engine->class != RENDER_CLASS)
+                       continue;
+
+               regs[0].value = intel_sseu_make_rpcs(i915, &ce->sseu);
+
+               err = gen8_modify_self(ce, regs, ARRAY_SIZE(regs));
+               if (err)
+                       return err;
+       }
return 0;
  }

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