perf: pin dashcamd to cores 0-3 (little cluster)

Previously ran unpinned (affinity mask 0xff) across all 8 cores. When it
landed on core 4 (controlsd) or 5 (plannerd/radard) or 7 (modeld), its
70MB/s frame copies and MP4 muxing caused cache/memory-bandwidth
contention with the RT-pinned processes. SCHED_FIFO prevented direct
preemption but not the cache thrash.

OMX offloads actual H.264 work to hardware so the main thread is
lightweight — fine on the little cluster.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

selfdrive/clearpilot/dashcamd.cc

@@ -38,7 +38,9 @@
 #include <cstdio>
 #include <ctime>
 #include <string>
+#include <errno.h>
 #include <signal.h>
+#include <sched.h>
 #include <execinfo.h>
 #include <sys/stat.h>
 #include <sys/resource.h>
@@ -121,6 +123,20 @@ int main(int argc, char *argv[]) {
   signal(SIGABRT, crash_handler);
   setpriority(PRIO_PROCESS, 0, -10);
 
+  // CLEARPILOT: pin to cores 0-3 (little cluster). Avoids cache/memory-bandwidth
+  // contention with the RT-pinned processes on the big cluster:
+  //   core 4 = controlsd, core 5 = plannerd/radard, core 7 = modeld.
+  // OMX offloads actual H.264 work to hardware, so the main thread just copies
+  // frames and muxes MP4 — fine on the little cluster.
+  cpu_set_t mask;
+  CPU_ZERO(&mask);
+  for (int i = 0; i < 4; i++) CPU_SET(i, &mask);
+  if (sched_setaffinity(0, sizeof(mask), &mask) != 0) {
+    LOGW("dashcamd: sched_setaffinity failed (%d), continuing unpinned", errno);
+  } else {
+    LOGW("dashcamd: pinned to cores 0-3");
+  }
+
   // Ensure base output directory exists
   mkdir(VIDEOS_BASE.c_str(), 0755);