commit 1e06ed69a7d10cad21f41b20f45540cf6cd0edbf
author Jagadeesh Pakaravoor <jpakaravoor@google.com> Wed Mar 31 18:25:24 2021 -0700
committer Jagadeesh Pakaravoor <jpakaravoor@google.com> Mon Apr 12 10:41:10 2021 -0700
tree ad3c7df4d4aa4517da56def5ae7e0d37d75852bc
parent c2d5b1bd4f1dce6eb3e200cc825b72b10d88bb14

Bump Surfaceflinger's binder threads to SCHED_FIFO

1) Set threads in Surfaceflinger's threadpool to have SCHED_FIFO policy
(and lowest RT priority). This is achieved by temporarily promoting the
priority of the thread creating the threadpool to the aforementioned
configuration.

2) Also set the minimum policy for the SF binder node to be SCHED_FIFO.

Test: presubmit
Bug: 183129340
Change-Id: I2df47fdc00fb0ae8937c30710243305cf018d830

services/surfaceflinger/main_surfaceflinger.cpp

diff --git a/services/surfaceflinger/main_surfaceflinger.cpp b/services/surfaceflinger/main_surfaceflinger.cpp
index 2b8424c..9686523 100644
--- a/services/surfaceflinger/main_surfaceflinger.cpp
+++ b/services/surfaceflinger/main_surfaceflinger.cpp
@@ -89,13 +89,47 @@
     // binder threads to 4.
     ProcessState::self()->setThreadPoolMaxThreadCount(4);
 
+    // The binder threadpool we start will inherit sched policy and priority
+    // of (this) creating thread. We want the binder thread pool to have
+    // SCHED_FIFO policy and priority 1 (lowest RT priority)
+    // Once the pool is created we reset this thread's priority back to
+    // original.
+    int newPriority = 0;
+    int origPolicy = sched_getscheduler(0);
+    struct sched_param origSchedParam;
+
+    int errorInPriorityModification = sched_getparam(0, &origSchedParam);
+    if (errorInPriorityModification == 0) {
+        int policy = SCHED_FIFO;
+        newPriority = sched_get_priority_min(policy);
+
+        struct sched_param param;
+        param.sched_priority = newPriority;
+
+        errorInPriorityModification = sched_setscheduler(0, policy, &param);
+    }
+
     // start the thread pool
     sp<ProcessState> ps(ProcessState::self());
     ps->startThreadPool();
 
+    // Reset current thread's policy and priority
+    if (errorInPriorityModification == 0) {
+        errorInPriorityModification = sched_setscheduler(0, origPolicy, &origSchedParam);
+    } else {
+        ALOGE("Failed to set SurfaceFlinger binder threadpool priority to SCHED_FIFO");
+    }
+
     // instantiate surfaceflinger
     sp<SurfaceFlinger> flinger = surfaceflinger::createSurfaceFlinger();
 
+    // Set the minimum policy of surfaceflinger node to be SCHED_FIFO.
+    // So any thread with policy/priority lower than {SCHED_FIFO, 1}, will run
+    // at least with SCHED_FIFO policy and priority 1.
+    if (errorInPriorityModification == 0) {
+        flinger->setMinSchedulerPolicy(SCHED_FIFO, newPriority);
+    }
+
     setpriority(PRIO_PROCESS, 0, PRIORITY_URGENT_DISPLAY);
 
     set_sched_policy(0, SP_FOREGROUND);