dm: set iothread nice value to PRIO_MIN

To improve the performance of the virtual device who utilizes iothread
(such as virtio-blk), this patch sets iothread nice value to PRIO_MIN,
so that it could get higher priority on scheduling.

This patch does:
 - introduce `set_thread_priority` to set the priority of the current running
   thread.
   The priority could be any value in the range PRIO_MIN to PRIO_MAX.
   Lower numerical value causes more favorable scheduling.

 - set iothread nice value to PRIO_MIN.

Tracked-On: #8612

Signed-off-by: Jian Jun Chen <jian.jun.chen@intel.com>
Signed-off-by: Shiqing Gao <shiqing.gao@intel.com>
Acked-by: Wang, Yu1 <yu1.wang@intel.com>

devicemodel/core/iothread.c

@@ -18,6 +18,7 @@
 #include "iothread.h"
 #include "log.h"
 #include "mevent.h"
+#include "dm.h"
 
 
 #define MEVENT_MAX 64
@@ -35,6 +36,8 @@ io_thread(void *arg)
 	int i, n;
 	struct iothread_ctx *ioctx_x = (struct iothread_ctx *)arg;
 
+	set_thread_priority(PRIO_IOTHREAD, true);
+
 	while(ioctx_x->started) {
 		n = epoll_wait(ioctx_x->epfd, eventlist, MEVENT_MAX, -1);
 		if (n < 0) {

devicemodel/core/main.c

@@ -247,6 +247,64 @@ high_bios_size(void)
 	return roundup2(size, 2 * MB);
 }
 
+/*
+ * set nice value of current pthread
+ * input range: [-20, 19]
+ * Lower priorities cause more favorable scheduling.
+ */
+void
+set_thread_priority(int priority, bool reset_on_fork)
+{
+	int ret, policy;
+	char tname[MAXCOMLEN + 1];
+	struct sched_param sp = { .sched_priority = 0 };
+
+	memset(tname, 0, sizeof(tname));
+	pthread_getname_np(pthread_self(), tname, sizeof(tname));
+
+	policy = sched_getscheduler(0);
+	if (policy == -1) {
+		pr_err("%s(%s), sched_getscheduler failed, errno = %d\n",
+			__func__, tname, errno);
+	}
+
+	if ((policy & SCHED_RESET_ON_FORK) && !reset_on_fork)
+		policy &= ~SCHED_RESET_ON_FORK;
+	else if (((policy & SCHED_RESET_ON_FORK) == 0) && reset_on_fork)
+		policy |= SCHED_RESET_ON_FORK;
+
+	ret = sched_setscheduler(0, policy, &sp);
+	if (ret == -1) {
+		pr_err("%s(%s), sched_setscheduler failed, errno = %d\n",
+			__func__, tname, errno);
+	}
+
+	errno = 0;
+	ret = getpriority(PRIO_PROCESS, 0);
+	if (errno && (ret == -1)) {
+		pr_err("%s(%s), getpriority failed, errno = %d\n",
+			__func__, tname, errno);
+	} else {
+		pr_info("%s(%s), orig prio = %d\n",
+			__func__, tname, ret);
+	}
+
+	ret = setpriority(PRIO_PROCESS, 0, priority);
+	if (ret) {
+		pr_err("%s(%s), setpriority failed, errno = %d\n",
+			__func__, tname, errno);
+	}
+
+	ret = getpriority(PRIO_PROCESS, 0);
+	if (ret != priority) {
+		pr_err("%s(%s), getpriority(%d) != setpriority(%d)\n",
+			__func__, tname, ret, priority);
+	} else {
+		pr_info("%s(%s), new priority = %d\n",
+			__func__, tname, ret);
+	}
+}
+
 static void *
 start_thread(void *param)
 {

devicemodel/include/dm.h

@@ -30,6 +30,8 @@
 #define	_DM_H_
 
 #include <stdbool.h>
+#include <sys/resource.h>
+
 #include "types.h"
 #include "dm_string.h"
 #include "acrn_common.h"
@@ -52,6 +54,14 @@ extern bool ssram;
 extern bool vtpm2;
 extern bool is_winvm;
 
+enum acrn_thread_prio {
+	PRIO_VCPU = PRIO_MIN,
+	PRIO_IOTHREAD = PRIO_MIN,
+	PRIO_VIRTIO_SND,
+	PRIO_VIRTIO_IPU,
+	PRIO_VIRTIO_GPU
+};
+
 /**
  * @brief Convert guest physical address to host virtual address
  *
@@ -67,4 +77,5 @@ int  guest_cpu_num(void);
 size_t high_bios_size(void);
 void init_debugexit(void);
 void deinit_debugexit(void);
+void set_thread_priority(int priority, bool reset_on_fork);
 #endif