asg: add a backoff to the guest

if the host is slow lets wait for it, don't priority invert

Change-Id: If680b01098c7f3918fa9dbcf6b0683ec49bbc888

1 files changed, 16 insertions, 0 deletions

diff --git a/system/OpenglSystemCommon/AddressSpaceStream.cpp b/system/OpenglSystemCommon/AddressSpaceStream.cpp
index ce7c7209..7c0f1546 100644
--- a/system/OpenglSystemCommon/AddressSpaceStream.cpp
+++ b/system/OpenglSystemCommon/AddressSpaceStream.cpp
@@ -388,7 +388,12 @@ ssize_t AddressSpaceStream::speculativeRead(unsigned char* readBuffer, size_t tr
     ensureType1Finished();
 
     size_t actuallyRead = 0;
+    size_t readIters = 0;
+    size_t backedOffIters = 0;
+    const size_t kSpeculativeReadBackoffIters = 10000000ULL;
     while (!actuallyRead) {
+        ++readIters;
+
         uint32_t readAvail =
             ring_buffer_available_read(
                 m_context.from_host_large_xfer.ring,
@@ -399,6 +404,11 @@ ssize_t AddressSpaceStream::speculativeRead(unsigned char* readBuffer, size_t tr
             continue;
         }
 
+        if (readAvail && readIters > kSpeculativeReadBackoffIters) {
+            usleep(10);
+            ++backedOffIters;
+        }
+
         uint32_t toRead = readAvail > trySize ?  trySize : readAvail;
 
         long stepsRead = ring_buffer_view_read(
@@ -413,6 +423,12 @@ ssize_t AddressSpaceStream::speculativeRead(unsigned char* readBuffer, size_t tr
         }
     }
 
+    if (backedOffIters > 0) {
+        ALOGE("%s: warning: backed off %zu times due to host slowness.\n",
+              __func__,
+              backedOffIters);
+    }
+
     return actuallyRead;
 }