drm/i915: Switch to kernel context before idling at runtime

We can reduce our exposure to random neutrinos by resting on the kernel
context having flushed out the user contexts to system memory and
beyond. The corollary is that we then we require two passes through the
idle handler to go to sleep, which on a truly idle system involves an
extra pass through the slow and irregular retire work handler.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180531082246.9763-1-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
index a8e7761cdc7d555c9798db08880ed96f6f5bce9d..15e86d34a81ce2cc68e54cffff5235a03074f8e7 100644 (file)
--- a/drivers/gpu/drm/i915/i915_debugfs.c
+++ b/drivers/gpu/drm/i915/i915_debugfs.c
@@ -4226,8 +4226,13 @@ i915_drop_caches_set(void *data, u64 val)
                i915_gem_shrink_all(dev_priv);
        fs_reclaim_release(GFP_KERNEL);
 
-       if (val & DROP_IDLE)
-               drain_delayed_work(&dev_priv->gt.idle_work);
+       if (val & DROP_IDLE) {
+               do {
+                       if (READ_ONCE(dev_priv->gt.active_requests))
+                               flush_delayed_work(&dev_priv->gt.retire_work);
+                       drain_delayed_work(&dev_priv->gt.idle_work);
+               } while (READ_ONCE(dev_priv->gt.awake));
+       }
 
        if (val & DROP_FREED)
                i915_gem_drain_freed_objects(dev_priv);

diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 530d6d0109b4d46dfff6c549da6d891310ad2de7..173d1e4ad963224105803e18f34c46c25ef42d3d 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -139,6 +139,8 @@ int i915_mutex_lock_interruptible(struct drm_device *dev)
 
 static u32 __i915_gem_park(struct drm_i915_private *i915)
 {
+       GEM_TRACE("\n");
+
        lockdep_assert_held(&i915->drm.struct_mutex);
        GEM_BUG_ON(i915->gt.active_requests);
        GEM_BUG_ON(!list_empty(&i915->gt.active_rings));
@@ -181,6 +183,8 @@ static u32 __i915_gem_park(struct drm_i915_private *i915)
 
 void i915_gem_park(struct drm_i915_private *i915)
 {
+       GEM_TRACE("\n");
+
        lockdep_assert_held(&i915->drm.struct_mutex);
        GEM_BUG_ON(i915->gt.active_requests);
 
@@ -193,6 +197,8 @@ void i915_gem_park(struct drm_i915_private *i915)
 
 void i915_gem_unpark(struct drm_i915_private *i915)
 {
+       GEM_TRACE("\n");
+
        lockdep_assert_held(&i915->drm.struct_mutex);
        GEM_BUG_ON(!i915->gt.active_requests);
 
@@ -3503,6 +3509,24 @@ i915_gem_idle_work_handler(struct work_struct *work)
        if (!READ_ONCE(dev_priv->gt.awake))
                return;
 
+       if (READ_ONCE(dev_priv->gt.active_requests))
+               return;
+
+       /*
+        * Flush out the last user context, leaving only the pinned
+        * kernel context resident. When we are idling on the kernel_context,
+        * no more new requests (with a context switch) are emitted and we
+        * can finally rest. A consequence is that the idle work handler is
+        * always called at least twice before idling (and if the system is
+        * idle that implies a round trip through the retire worker).
+        */
+       mutex_lock(&dev_priv->drm.struct_mutex);
+       i915_gem_switch_to_kernel_context(dev_priv);
+       mutex_unlock(&dev_priv->drm.struct_mutex);
+
+       GEM_TRACE("active_requests=%d (after switch-to-kernel-context)\n",
+                 READ_ONCE(dev_priv->gt.active_requests));
+
        /*
         * Wait for last execlists context complete, but bail out in case a
         * new request is submitted. As we don't trust the hardware, we
@@ -4913,11 +4937,9 @@ static void assert_kernel_context_is_current(struct drm_i915_private *i915)
 
 void i915_gem_sanitize(struct drm_i915_private *i915)
 {
-       if (i915_terminally_wedged(&i915->gpu_error)) {
-               mutex_lock(&i915->drm.struct_mutex);
+       mutex_lock(&i915->drm.struct_mutex);
+       if (i915_terminally_wedged(&i915->gpu_error))
                i915_gem_unset_wedged(i915);
-               mutex_unlock(&i915->drm.struct_mutex);
-       }
 
        /*
         * If we inherit context state from the BIOS or earlier occupants
@@ -4929,6 +4951,9 @@ void i915_gem_sanitize(struct drm_i915_private *i915)
         */
        if (INTEL_GEN(i915) >= 5 && intel_has_gpu_reset(i915))
                WARN_ON(intel_gpu_reset(i915, ALL_ENGINES));
+
+       i915_gem_contexts_lost(i915);
+       mutex_unlock(&i915->drm.struct_mutex);
 }
 
 int i915_gem_suspend(struct drm_i915_private *dev_priv)
@@ -4964,7 +4989,6 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
 
                assert_kernel_context_is_current(dev_priv);
        }
-       i915_gem_contexts_lost(dev_priv);
        mutex_unlock(&dev->struct_mutex);
 
        intel_uc_suspend(dev_priv);
@@ -5017,6 +5041,8 @@ int i915_gem_suspend(struct drm_i915_private *dev_priv)
 
 void i915_gem_resume(struct drm_i915_private *i915)
 {
+       GEM_TRACE("\n");
+
        WARN_ON(i915->gt.awake);
 
        mutex_lock(&i915->drm.struct_mutex);

diff --git a/drivers/gpu/drm/i915/i915_gem_context.c b/drivers/gpu/drm/i915/i915_gem_context.c
index 45393f6e0208b5140816fbb8cdab860dd50ac0ec..81f086397d10b8499ae4b7fab29fb585b6f25ab1 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_context.c
+++ b/drivers/gpu/drm/i915/i915_gem_context.c
@@ -649,7 +649,7 @@ int i915_gem_switch_to_kernel_context(struct drm_i915_private *i915)
        struct intel_engine_cs *engine;
        enum intel_engine_id id;
 
-       GEM_TRACE("\n");
+       GEM_TRACE("awake?=%s\n", yesno(i915->gt.awake));
 
        lockdep_assert_held(&i915->drm.struct_mutex);
        GEM_BUG_ON(!i915->kernel_context);