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[Threading/Linux] Add fallback to nice values

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SCHED_FIFO requires CAP_SYS_NICE or root, try SCHED_FIFO first for real-time
priority control, then fall back to setpriority() nice values if permission
is denied.
This commit is contained in:
Herman S.
2026-04-13 16:23:27 +09:00
parent 844cc6e2ed
commit 763b160c7a
1 changed files with 41 additions and 19 deletions
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60
src/xenia/base/threading_posix.cc
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@@ -18,6 +18,7 @@
#include <sched.h>
#include <semaphore.h>
#include <signal.h>
#include <sys/resource.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <array>
@@ -611,6 +612,7 @@ class PosixCondition<Thread> final : public PosixConditionBase {
/// Thread::GetCurrentThread() on the main thread
explicit PosixCondition(pthread_t thread)
: thread_(thread),
tid_(static_cast<pid_t>(syscall(SYS_gettid))),
signaled_(false),
exit_code_(0),
state_(State::kRunning),
@@ -742,31 +744,48 @@ class PosixCondition<Thread> final : public PosixConditionBase {
int priority() const {
WaitStarted();
int policy;
sched_param param{};
int ret = pthread_getschedparam(thread_, &policy, &param);
if (ret != 0) {
return -1;
if (!fifo_failed_) {
int policy;
sched_param param{};
int ret = pthread_getschedparam(thread_, &policy, &param);
if (ret != 0) {
return -1;
}
return param.sched_priority;
}
return param.sched_priority;
// When using nice values, map back to the SCHED_FIFO range (1-32)
// so callers see a consistent priority space.
int nice_val = getpriority(PRIO_PROCESS, tid_);
// nice -19..19 → fifo 32..1
return 16 - nice_val;
}
void set_priority(int new_priority) const {
WaitStarted();
sched_param param{};
param.sched_priority = new_priority;
int res = pthread_setschedparam(thread_, SCHED_FIFO, &param);
if (res != 0) {
switch (res) {
case EPERM:
XELOGW("Permission denied while setting priority");
break;
case EINVAL:
assert_always();
default:
XELOGW("Unknown error while setting priority");
if (!fifo_failed_) {
// Try real-time SCHED_FIFO for best priority control.
sched_param param{};
param.sched_priority = new_priority;
int res = pthread_setschedparam(thread_, SCHED_FIFO, &param);
if (res == 0) {
return;
}
if (res == EPERM) {
fifo_failed_ = true;
} else {
XELOGW("Unexpected error {} while setting SCHED_FIFO priority", res);
fifo_failed_ = true;
}
}
// Fall back to nice values under SCHED_OTHER.
// Map SCHED_FIFO range (1-32) to nice range (19 to -19).
// Center: fifo 16 → nice 0.
int nice_val = 16 - new_priority;
// Clamp to valid nice range.
if (nice_val < -20) nice_val = -20;
if (nice_val > 19) nice_val = 19;
if (tid_ > 0) {
setpriority(PRIO_PROCESS, tid_, nice_val);
}
}
@@ -930,6 +949,8 @@ class PosixCondition<Thread> final : public PosixConditionBase {
sem_destroy(&suspend_sem_);
}
pthread_t thread_;
pid_t tid_ = 0; // Kernel TID for setpriority() fallback
mutable bool fifo_failed_ = false; // True after SCHED_FIFO was rejected
bool signaled_;
int exit_code_;
State state_; // Protected by state_mutex_
@@ -1243,6 +1264,7 @@ void* PosixCondition<Thread>::ThreadStartRoutine(void* parameter) {
delete start_data;
current_thread_ = thread;
thread->handle_.tid_ = static_cast<pid_t>(syscall(SYS_gettid));
{
std::unique_lock lock(thread->handle_.state_mutex_);
thread->handle_.state_ =