commit 151f782ee4c5269e331bc97ef8a60c0cae1d66da
author Austin Schuh <austin.linux@gmail.com> Sat Mar 16 12:52:32 2024 -0700
committer Austin Schuh <austin.linux@gmail.com> Sat Mar 16 13:01:37 2024 -0700
tree 6db3e25d147f2e1ae4f8f5d1004c8c48772b9b32
parent d8362d568d26dfb6069dc1b6332f1063e478dbc2

Speed up LocklessQueueWakeUpper::Wakeup by inlining sched_setscheduler

We were checking and updating the soft limits (and taking no action...)
every time we sent a message which needed PI boosting (sender is lower
priority than the receiver).

Stop checking everything else and only do the sched_setscheduler call
inline.  This takes ~50% CPU to ~25% CPU for our CAN processing code
processing 8k wakeups/sec.

Change-Id: I92fb5a89f6edcfaa9a47257eda401b5c05b3226a
Signed-off-by: Austin Schuh <austin.linux@gmail.com>

aos/ipc_lib/lockless_queue.cc

diff --git a/aos/ipc_lib/lockless_queue.cc b/aos/ipc_lib/lockless_queue.cc
index a26b564..9d14d8f 100644
--- a/aos/ipc_lib/lockless_queue.cc
+++ b/aos/ipc_lib/lockless_queue.cc
@@ -21,6 +21,7 @@
 
 DEFINE_bool(dump_lockless_queue_data, false,
             "If true, print the data out when dumping the queue.");
+DECLARE_bool(skip_realtime_scheduler);
 
 namespace aos::ipc_lib {
 namespace {
@@ -813,7 +814,19 @@
     // Boost if we are RT and there is a higher priority sender out there.
     // Otherwise we might run into priority inversions.
     if (max_priority > current_priority && current_priority > 0) {
-      SetCurrentThreadRealtimePriority(max_priority);
+      // Inline the setscheduler call rather than using aos/realtime.h.  This is
+      // quite performance sensitive, and halves the time needed to send a
+      // message when pi boosting is in effect.
+      if (!FLAGS_skip_realtime_scheduler) {
+        // TODO(austin): Do we need to boost the soft limit here too like we
+        // were before?
+        struct sched_param param;
+        param.sched_priority = max_priority;
+        PCHECK(sched_setscheduler(0, SCHED_FIFO, &param) == 0)
+            << ": changing to SCHED_FIFO with " << max_priority
+            << ", if you want to bypass this check for testing, use "
+               "--skip_realtime_scheduler";
+      }
     }
 
     // Build up the siginfo to send.
@@ -842,7 +855,14 @@
 
     // Drop back down if we were boosted.
     if (max_priority > current_priority && current_priority > 0) {
-      SetCurrentThreadRealtimePriority(current_priority);
+      if (!FLAGS_skip_realtime_scheduler) {
+        struct sched_param param;
+        param.sched_priority = current_priority;
+        PCHECK(sched_setscheduler(0, SCHED_FIFO, &param) == 0)
+            << ": changing to SCHED_FIFO with " << max_priority
+            << ", if you want to bypass this check for testing, use "
+               "--skip_realtime_scheduler";
+      }
     }
   }