From c3fe0f4000139c6e46e4dbea1346c0e3855e17ac Mon Sep 17 00:00:00 2001
From: Evan Klitzke <evan@eklitzke.org>
Date: Mon, 2 Dec 2019 18:18:17 -0800
Subject: [PATCH] use SCHED_BATCH scheduling priority for indexing threads

---
 src/messages/initialize.cc |  1 +
 src/platform.hh            |  2 ++
 src/platform_posix.cc      | 22 ++++++++++++++++++++++
 src/platform_win.cc        |  2 ++
 4 files changed, 27 insertions(+)

diff --git a/src/messages/initialize.cc b/src/messages/initialize.cc
index b015d98d..c3380642 100644
--- a/src/messages/initialize.cc
+++ b/src/messages/initialize.cc
@@ -255,6 +255,7 @@ void *indexer(void *arg_) {
   delete arg;
   std::string name = "indexer" + std::to_string(idx);
   set_thread_name(name.c_str());
+  setBatchPriority();
   pipeline::indexer_Main(h->manager, h->vfs, h->project, h->wfiles);
   pipeline::threadLeave();
   return nullptr;
diff --git a/src/platform.hh b/src/platform.hh
index 5fa7cfe7..dd81ae60 100644
--- a/src/platform.hh
+++ b/src/platform.hh
@@ -17,4 +17,6 @@ void freeUnusedMemory();
 void traceMe();
 
 void spawnThread(void *(*fn)(void *), void *arg);
+
+void setBatchPriority();
 } // namespace ccls
diff --git a/src/platform_posix.cc b/src/platform_posix.cc
index 6fd04995..c8556882 100644
--- a/src/platform_posix.cc
+++ b/src/platform_posix.cc
@@ -4,6 +4,7 @@
 #if defined(__unix__) || defined(__APPLE__)
 #include "platform.hh"
 
+#include "log.hh"
 #include "utils.hh"
 
 #include <assert.h>
@@ -17,6 +18,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <pthread.h>
+#include <sched.h>
 #include <signal.h>
 #include <sys/resource.h>
 #include <sys/stat.h>
@@ -75,6 +77,26 @@ void spawnThread(void *(*fn)(void *), void *arg) {
   pthread_create(&thd, &attr, fn, arg);
   pthread_attr_destroy(&attr);
 }
+
+void setBatchPriority() {
+#ifdef SCHED_BATCH
+  pid_t this_thread_id = gettid();
+
+  // get a sched_param with the existing thread sched_priority
+  errno = 0;
+  struct sched_param p;
+  p.sched_priority = getpriority(PRIO_PROCESS, this_thread_id);
+  if (p.sched_priority == -1 && errno != 0) {
+    LOG_S(ERROR) << "failed to getpriority(): " << strerror(errno);
+    return;
+  }
+
+  // retain the existing sched_priority, but use SCHED_BATCH policy
+  if (sched_setscheduler(this_thread_id, SCHED_BATCH, &p) == -1) {
+    LOG_S(ERROR) << "failed to sched_setscheduler(): " << strerror(errno);
+  }
+}
+#endif
 } // namespace ccls
 
 #endif
diff --git a/src/platform_win.cc b/src/platform_win.cc
index 9fa28e3b..29ba5f9a 100644
--- a/src/platform_win.cc
+++ b/src/platform_win.cc
@@ -48,6 +48,8 @@ void traceMe() {}
 void spawnThread(void *(*fn)(void *), void *arg) {
   std::thread(fn, arg).detach();
 }
+
+void setBatchPriority() {}
 } // namespace ccls
 
 #endif