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Make some changes to SDL_SetThreadPriority to try and have SDL transparently handle more of the work.

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1. Comment that SDL_SetThreadPriority will make any necessary system changes when applying priority.
2. Add a hint to override SDL's default behavior for scheduler policy.
3. Modify the pthreads SDL_SetThreadPriority so that instead of just using the current thread scheduler policy it will change it to a policy that should work best for the requested priority.
4. Add hint checks in SDL_SetThreadPriority so that #3 can be overridden if desired.
5. Modify the Linux SDL_SetThreadPriority so that in the case that policy, either by SDL defaults or from the hint, is a realtime policy it uses the realtime rtkit API.
6. Prior to calling rtkit on Linux make the necessary thread state changes that rtkit requires.  Currently this is done every time as it isn't expected that SDL_SetThreadPriority will be called repeatedly for a thread.
This commit is contained in:
Sam Lantinga 2020-05-26 13:19:19 -07:00
parent f16e6bfa8e
commit abd5841850
4 changed files with 241 additions and 17 deletions
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66
src/thread/pthread/SDL_systhread.c
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@ -184,34 +184,71 @@ SDL_ThreadID(void)
return ((SDL_threadID) pthread_self());
}
#if __LINUX__
/**
\brief Sets the SDL priority (not nice level) for a thread, using setpriority() if appropriate, and RealtimeKit if available.
Differs from SDL_LinuxSetThreadPriority in also taking the desired scheduler policy,
such as SCHED_OTHER or SCHED_RR.
\return 0 on success, or -1 on error.
*/
extern DECLSPEC int SDLCALL SDL_LinuxSetThreadPriorityAndPolicy(Sint64 threadID, int sdlPriority, int schedPolicy);
#endif
int
SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
{
#if __NACL__ || __RISCOS__
/* FIXME: Setting thread priority does not seem to be supported in NACL */
return 0;
#elif __LINUX__
int value;
pid_t thread = syscall(SYS_gettid);
if (priority == SDL_THREAD_PRIORITY_LOW) {
value = 19;
} else if (priority == SDL_THREAD_PRIORITY_HIGH) {
value = -10;
} else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
value = -20;
} else {
value = 0;
}
return SDL_LinuxSetThreadPriority(thread, value);
#else
struct sched_param sched;
int policy;
int pri_policy;
pthread_t thread = pthread_self();
const char *policyhint = SDL_GetHint(SDL_HINT_THREAD_PRIORITY_POLICY);
if (pthread_getschedparam(thread, &policy, &sched) != 0) {
return SDL_SetError("pthread_getschedparam() failed");
}
/* Higher priority levels may require changing the pthread scheduler policy
* for the thread. SDL will make such changes by default but there is
* also a hint allowing that behavior to be overridden. */
switch (priority) {
case SDL_THREAD_PRIORITY_LOW:
case SDL_THREAD_PRIORITY_NORMAL:
pri_policy = SCHED_OTHER;
break;
case SDL_THREAD_PRIORITY_HIGH:
case SDL_THREAD_PRIORITY_TIME_CRITICAL:
pri_policy = SCHED_RR;
break;
default:
pri_policy = policy;
break;
}
if (policyhint) {
if (SDL_strcmp(policyhint, "current") == 0) {
/* Leave current thread scheduler policy unchanged */
} else if (SDL_strcmp(policyhint, "other") == 0) {
policy = SCHED_OTHER;
} else if (SDL_strcmp(policyhint, "rr") == 0) {
policy = SCHED_RR;
} else if (SDL_strcmp(policyhint, "fifo") == 0) {
policy = SCHED_FIFO;
} else {
policy = pri_policy;
}
} else {
policy = pri_policy;
}
#if __LINUX__
pid_t thread = syscall(SYS_gettid);
return SDL_LinuxSetThreadPriorityAndPolicy(thread, priority, policy);
#else
if (priority == SDL_THREAD_PRIORITY_LOW) {
sched.sched_priority = sched_get_priority_min(policy);
} else if (priority == SDL_THREAD_PRIORITY_TIME_CRITICAL) {
@ -242,6 +279,7 @@ SDL_SYS_SetThreadPriority(SDL_ThreadPriority priority)
}
return 0;
#endif /* linux */
#endif /* #if __NACL__ || __RISCOS__ */
}
void