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realtime: request SCHED_RR using CAP_SYS_NICE

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Try to gain SCHED_RR (round-robin) realtime scheduling privileges before
starting the server. This requires CAP_SYS_NICE on Linux systems.
We additionally register a pthread_atfork callback which resets the
scheduling class back to SCHED_OTHER (the Linux system default).

Due to CAP_SYS_NICE, setting RLIMIT_RTPRIO has no effect on the process
as documented within man 7 sched (from Linux):

  Privileged (CAP_SYS_NICE) threads ignore the RLIMIT_RTPRIO limit;
  as with older kernels, they can make arbitrary changes to
  scheduling policy and priority. See getrlimit(2) for further
  information on RLIMIT_RTPRIO

Note that this requires the sway distribution packagers to set the
CAP_SYS_NICE capability on the sway binary.

Supersedes #6992
This commit is contained in:
Rouven Czerwinski 2022-05-13 20:30:19 +02:00 committed by Kenny Levinsen
parent 3f600565e4
commit a3a82efbf6
4 changed files with 45 additions and 0 deletions
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2
include/sway/server.h
View file

@ -173,4 +173,6 @@ void handle_pointer_constraint(struct wl_listener *listener, void *data);
void xdg_activation_v1_handle_request_activate(struct wl_listener *listener,
void *data);
void set_rr_scheduling(void);
#endif

2
sway/main.c
View file

@ -413,6 +413,8 @@ int main(int argc, char **argv) {
goto shutdown;
}
set_rr_scheduling();
if (!server_start(&server)) {
sway_terminate(EXIT_FAILURE);
goto shutdown;

1
sway/meson.build
View file

@ -7,6 +7,7 @@ sway_sources = files(
'ipc-server.c',
'lock.c',
'main.c',
'realtime.c',
'server.c',
'swaynag.c',
'xdg_activation_v1.c',

40
sway/realtime.c Normal file
View file

@ -0,0 +1,40 @@
#include <sys/resource.h>
#include <sched.h>
#include <unistd.h>
#include <pthread.h>
#include "sway/server.h"
#include "log.h"
static void child_fork_callback(void) {
struct sched_param param;
param.sched_priority = 0;
int ret = pthread_setschedparam(pthread_self(), SCHED_OTHER, &param);
if (ret != 0) {
sway_log(SWAY_ERROR, "Failed to reset scheduler policy on fork");
}
}
void set_rr_scheduling(void) {
int prio = sched_get_priority_min(SCHED_RR);
int old_policy;
int ret;
struct sched_param param;
ret = pthread_getschedparam(pthread_self(), &old_policy, &param);
if (ret != 0) {
sway_log(SWAY_DEBUG, "Failed to get old scheduling priority");
return;
}
param.sched_priority = prio;
ret = pthread_setschedparam(pthread_self(), SCHED_RR, &param);
if (ret != 0) {
sway_log(SWAY_INFO, "Failed to set scheduling priority to %d", prio);
return;
}
pthread_atfork(NULL, NULL, child_fork_callback);
}