Linux: Change minimum priority threads from SCHED_IDLE to nice 19 SCHED_BATCH.

SCHED_IDLE on linux can lead to extraordinarily long periods of no scheduling
leading to starvation of minimum priority threads for such an extended period
that it can eventually lead to GUI stalls. Switch to renicing the threads to
the lowest priority and use the SCHED_BATCH scheduling policy which is a hint
to the scheduler that this is latency insensitive thread instead. This change
has been confirmed to address unexpected GUI related stalls in mesa
applications across a range of different linux kernels.

Signed-off-by: Con Kolivas <kernel@kolivas.org>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4912>

diff --git a/src/util/u_queue.c b/src/util/u_queue.c
index 4049a4c7692e90655d3020e12da35c277531ae86..8f6dc08b3326a9d5f4475c238ccd9f8286fe0e56 100644 (file)
--- a/src/util/u_queue.c
+++ b/src/util/u_queue.c
@@ -33,6 +33,13 @@
 #include "util/u_thread.h"
 #include "u_process.h"
 
+#if defined(__linux__)
+#include <sys/time.h>
+#include <sys/resource.h>
+#include <sys/syscall.h>
+#endif
+
+
 /* Define 256MB */
 #define S_256MB (256 * 1024 * 1024)
 
@@ -258,6 +265,13 @@ util_queue_thread_func(void *input)
    }
 #endif
 
+#if defined(__linux__)
+   if (queue->flags & UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY) {
+      /* The nice() function can only set a maximum of 19. */
+      setpriority(PRIO_PROCESS, syscall(SYS_gettid), 19);
+   }
+#endif
+
    if (strlen(queue->name) > 0) {
       char name[16];
       snprintf(name, sizeof(name), "%s%i", queue->name, thread_index);
@@ -331,16 +345,17 @@ util_queue_create_thread(struct util_queue *queue, unsigned index)
    }
 
    if (queue->flags & UTIL_QUEUE_INIT_USE_MINIMUM_PRIORITY) {
-#if defined(__linux__) && defined(SCHED_IDLE)
+#if defined(__linux__) && defined(SCHED_BATCH)
       struct sched_param sched_param = {0};
 
       /* The nice() function can only set a maximum of 19.
-       * SCHED_IDLE is the same as nice = 20.
+       * SCHED_BATCH gives the scheduler a hint that this is a latency
+       * insensitive thread.
        *
        * Note that Linux only allows decreasing the priority. The original
        * priority can't be restored.
        */
-      pthread_setschedparam(queue->threads[index], SCHED_IDLE, &sched_param);
+      pthread_setschedparam(queue->threads[index], SCHED_BATCH, &sched_param);
 #endif
    }
    return true;