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Fix process randomly getting killed when SDL_THREAD_PRIORITY_HIGH/TIME_CRITICAL is set

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When we request realtime priority from rtkit, we have a rttime limit. If we exceed
that limit, the kernel will send SIGKILL to the process to terminate it.

This isn't something that most high priority processes will want, only processes
that selectively opt into SCHED_RR/FIFO through SDL_HINT_THREAD_PRIORITY_POLICY
should be subject to this level of scrutiny.

This change:
  * Switches non-apple posix OSs to use SCHED_OTHER instead of SCHED_RR
for SDL_THREAD_PRIORITY_HIGH/SDL_THREAD_PRIORITY_TIME_CRITICAL.
  * Fixes using a hardcoded RLIMIT_RTTIME, instead queries it from rtkit
  * Only sets RLIMIT_RTTIME for MakeRealtime rtkit requests
  * Adds a note regarding the possible SIGKILL with SDL_HINT_THREAD_PRIORITY_POLICY
  * Introduces SDL_HINT_THREAD_FORCE_REALTIME_TIME_CRITICAL to allow apps to acquire realtime scheduling policies on Linux
This commit is contained in:
Sam Lantinga
2020-11-11 08:47:18 -08:00
parent 59795822d0
commit 07eae7d670
3 changed files with 41 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files

22
src/core/linux/SDL_threadprio.c
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@@ -50,6 +50,7 @@
static pthread_once_t rtkit_initialize_once = PTHREAD_ONCE_INIT;
static Sint32 rtkit_min_nice_level = -20;
static Sint32 rtkit_max_realtime_priority = 99;
static Sint64 rtkit_max_rttime_usec = 200000;
static void
rtkit_initialize()
@@ -67,10 +68,16 @@ rtkit_initialize()
DBUS_TYPE_INT32, &rtkit_max_realtime_priority)) {
rtkit_max_realtime_priority = 99;
}
/* Try getting maximum rttime allowed by rtkit: exceeding this value will result in SIGKILL */
if (!dbus || !SDL_DBus_QueryPropertyOnConnection(dbus->system_conn, RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "RTTimeUSecMax",
DBUS_TYPE_INT64, &rtkit_max_rttime_usec)) {
rtkit_max_rttime_usec = 200000;
}
}
static SDL_bool
rtkit_initialize_thread()
rtkit_initialize_realtime_thread()
{
// Following is an excerpt from rtkit README that outlines the requirements
// a thread must meet before making rtkit requests:
@@ -107,7 +114,8 @@ rtkit_initialize_thread()
}
// Current rtkit allows a max of 200ms right now
rlimit.rlim_cur = rlimit.rlim_max = 100000;
rlimit.rlim_max = rtkit_max_rttime_usec;
rlimit.rlim_cur = rlimit.rlim_max / 2;
err = setrlimit(nLimit, &rlimit);
if (err)
{
@@ -142,14 +150,6 @@ rtkit_setpriority_nice(pid_t thread, int nice_level)
if (si32 < rtkit_min_nice_level)
si32 = rtkit_min_nice_level;
// We always perform the thread state changes necessary for rtkit.
// This wastes some system calls if the state is already set but
// typically code sets a thread priority and leaves it so it's
// not expected that this wasted effort will be an issue.
// We also do not quit if this fails, we let the rtkit request
// go through to determine whether it really needs to fail or not.
rtkit_initialize_thread();
if (!dbus || !SDL_DBus_CallMethodOnConnection(dbus->system_conn,
RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "MakeThreadHighPriority",
DBUS_TYPE_UINT64, &ui64, DBUS_TYPE_INT32, &si32, DBUS_TYPE_INVALID,
@@ -177,7 +177,7 @@ rtkit_setpriority_realtime(pid_t thread, int rt_priority)
// not expected that this wasted effort will be an issue.
// We also do not quit if this fails, we let the rtkit request
// go through to determine whether it really needs to fail or not.
rtkit_initialize_thread();
rtkit_initialize_realtime_thread();
if (!dbus || !SDL_DBus_CallMethodOnConnection(dbus->system_conn,
RTKIT_DBUS_NODE, RTKIT_DBUS_PATH, RTKIT_DBUS_INTERFACE, "MakeThreadRealtime",