drm_hwcomposer: Implement BI and FB caching

This allows saving for about 2-6% of frame time spending in the HWC API
thread (value depends on CPU maturity).

Framework does not create a new buffer for every frame. Instead in 98%
of cases it sends the same buffers over and over (doing circular
shifting of the swapchain).

We can avoid redundant BufferInfo getting and FrameBuffer importing for
the whole layer.

To do this properly first we have to ensure we're having a deal with the
swapchain, not a set of unique buffers. This procedure internally called
the swap chain reassembling.

After we ensure CLIENT is using swapchain, we can safely store BI and
FB for every chain element and reuse it.

Example for single layer:

Frame # |  Buffer Unique ID |     State
 --     | --                | --
      1 |               301 | Reassembling...
      2 |               302 | Reassembling...
      3 |               303 | Reassembling...
      4 |               301 | Caching... (Chain reassembled!)
      5 |               302 | Caching...
      6 |               303 | Caching...
      7 |               301 | Reusing cached data
      8 |               302 | Reusing cached data
      9 |               303 | Reusing cached data
    ... |               ... | ...................
    999 |               304 | Not in cache, purge the cache.
   1000 |               305 | Reassembling...

Signed-off-by: Roman Stratiienko <roman.o.stratiienko@globallogic.com>

3 files changed, 100 insertions, 0 deletions

diff --git a/hwc2_device/HwcDisplay.cpp b/hwc2_device/HwcDisplay.cpp
index 02df28c..76e2745 100644
--- a/hwc2_device/HwcDisplay.cpp
+++ b/hwc2_device/HwcDisplay.cpp
@@ -602,6 +602,7 @@ HWC2::Error HwcDisplay::SetClientTarget(buffer_handle_t target,
    * https://cs.android.com/android/platform/superproject/+/master:hardware/interfaces/graphics/composer/2.1/utils/hal/include/composer-hal/2.1/ComposerClient.h;l=350;drc=944b68180b008456ed2eb4d4d329e33b19bd5166
    */
   if (target == nullptr) {
+    client_layer_.SwChainClearCache();
     return HWC2::Error::None;
   }
 
diff --git a/hwc2_device/HwcLayer.cpp b/hwc2_device/HwcLayer.cpp
index f57ad9b..c278732 100644
--- a/hwc2_device/HwcLayer.cpp
+++ b/hwc2_device/HwcLayer.cpp
@@ -174,6 +174,11 @@ void HwcLayer::ImportFb() {
 
   layer_data_.fb = {};
 
+  auto unique_id = BufferInfoGetter::GetInstance()->GetUniqueId(buffer_handle_);
+  if (unique_id && SwChainGetBufferFromCache(*unique_id)) {
+    return;
+  }
+
   layer_data_.bi = BufferInfoGetter::GetInstance()->GetBoInfo(buffer_handle_);
   if (!layer_data_.bi) {
     ALOGW("Unable to get buffer information (0x%p)", buffer_handle_);
@@ -191,6 +196,10 @@ void HwcLayer::ImportFb() {
     fb_import_failed_ = true;
     return;
   }
+
+  if (unique_id) {
+    SwChainAddCurrentBuffer(*unique_id);
+  }
 }
 
 void HwcLayer::PopulateLayerData(bool test) {
@@ -211,4 +220,75 @@ void HwcLayer::PopulateLayerData(bool test) {
   }
 }
 
+/* SwapChain Cache */
+
+bool HwcLayer::SwChainGetBufferFromCache(BufferUniqueId unique_id) {
+  if (swchain_lookup_table_.count(unique_id) == 0) {
+    return false;
+  }
+
+  int seq = swchain_lookup_table_[unique_id];
+
+  if (swchain_cache_.count(seq) == 0) {
+    return false;
+  }
+
+  auto& el = swchain_cache_[seq];
+  if (!el.bi) {
+    return false;
+  }
+
+  layer_data_.bi = el.bi;
+  layer_data_.fb = el.fb;
+
+  return true;
+}
+
+void HwcLayer::SwChainReassemble(BufferUniqueId unique_id) {
+  if (swchain_lookup_table_.count(unique_id) != 0) {
+    if (swchain_lookup_table_[unique_id] ==
+        int(swchain_lookup_table_.size()) - 1) {
+      /* Skip same buffer */
+      return;
+    }
+    if (swchain_lookup_table_[unique_id] == 0) {
+      swchain_reassembled_ = true;
+      return;
+    }
+    /* Tracking error */
+    SwChainClearCache();
+    return;
+  }
+
+  swchain_lookup_table_[unique_id] = int(swchain_lookup_table_.size());
+}
+
+void HwcLayer::SwChainAddCurrentBuffer(BufferUniqueId unique_id) {
+  if (!swchain_reassembled_) {
+    SwChainReassemble(unique_id);
+  }
+
+  if (swchain_reassembled_) {
+    if (swchain_lookup_table_.count(unique_id) == 0) {
+      SwChainClearCache();
+      return;
+    }
+
+    int seq = swchain_lookup_table_[unique_id];
+
+    if (swchain_cache_.count(seq) == 0) {
+      swchain_cache_[seq] = {};
+    }
+
+    swchain_cache_[seq].bi = layer_data_.bi;
+    swchain_cache_[seq].fb = layer_data_.fb;
+  }
+}
+
+void HwcLayer::SwChainClearCache() {
+  swchain_cache_.clear();
+  swchain_lookup_table_.clear();
+  swchain_reassembled_ = false;
+}
+
 }  // namespace android
\ No newline at end of file
diff --git a/hwc2_device/HwcLayer.h b/hwc2_device/HwcLayer.h
index 92e9476..41b3dbb 100644
--- a/hwc2_device/HwcLayer.h
+++ b/hwc2_device/HwcLayer.h
@@ -19,6 +19,7 @@
 
 #include <hardware/hwcomposer2.h>
 
+#include "bufferinfo/BufferInfoGetter.h"
 #include "compositor/LayerData.h"
 
 namespace android {
@@ -118,6 +119,24 @@ class HwcLayer {
   void ImportFb();
   bool bi_get_failed_{};
   bool fb_import_failed_{};
+
+  /* SwapChain Cache */
+ public:
+  void SwChainClearCache();
+
+ private:
+  struct SwapChainElement {
+    std::optional<BufferInfo> bi;
+    std::shared_ptr<DrmFbIdHandle> fb;
+  };
+
+  bool SwChainGetBufferFromCache(BufferUniqueId unique_id);
+  void SwChainReassemble(BufferUniqueId unique_id);
+  void SwChainAddCurrentBuffer(BufferUniqueId unique_id);
+
+  std::map<int /*seq_no*/, SwapChainElement> swchain_cache_;
+  std::map<BufferUniqueId, int /*seq_no*/> swchain_lookup_table_;
+  bool swchain_reassembled_{};
 };
 
 }  // namespace android