[PATCH 2/3] virprocess: add the SCHED_DEADLINE scheduling policy

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Tasks associated to virtual CPUs, IO Threads and Emulator processes
can be created with the SCHED_DEADLINE policy. The policy is described
in details here: https://docs.kernel.org/scheduler/sched-deadline.html

It requires the following parameters (all in nanoseconds):
1) runtime
2) deadline
3) period

It must always holds that: runtime <= deadline <= period.

The kernel enforces that the values stay within [1024, 2^63-1].
Note, however, that a smaller range could be set (or be already set
by  default) via sysctl (see kernel.sched_deadline_period_max_us and
kernel.sched_deadline_period_min_us).

All the three parameters are mandatory but period can be set to 0,
in which case it will set to the same value of deadline.

Signed-off-by: Sasha Algisi <sasha.algisi@xxxxxxxxxxxx>
Signed-off-by: Dario Faggioli <dfaggioli@xxxxxxxx>
---
 src/ch/ch_process.c     |  3 +-
 src/conf/domain_conf.h  |  3 ++
 src/qemu/qemu_process.c |  8 +++-
 src/util/virprocess.c   | 84 +++++++++++++++++++++++++++++++++++++++--
 src/util/virprocess.h   |  6 ++-
 5 files changed, 97 insertions(+), 7 deletions(-)

diff --git a/src/ch/ch_process.c b/src/ch/ch_process.c
index 77f55e777b..a40d188aac 100644
--- a/src/ch/ch_process.c
+++ b/src/ch/ch_process.c
@@ -293,7 +293,8 @@ virCHProcessSetupPid(virDomainObj *vm,
     /* Set scheduler type and priority, but not for the main thread. */
     if (sched &&
         nameval != VIR_CGROUP_THREAD_EMULATOR &&
-        virProcessSetScheduler(pid, sched->policy, sched->priority) < 0)
+        virProcessSetScheduler(pid, sched->policy, sched->priority,
+                               sched->runtime, sched->deadline, sched->period) < 0)
         goto cleanup;
 
     ret = 0;
diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
index 060c395943..c3d1a1b65d 100644
--- a/src/conf/domain_conf.h
+++ b/src/conf/domain_conf.h
@@ -2454,6 +2454,9 @@ typedef enum {
 struct _virDomainThreadSchedParam {
     virProcessSchedPolicy policy;
     int priority;
+    uint64_t runtime;
+    uint64_t deadline;
+    uint64_t period;
 };
 
 struct _virDomainTimerCatchupDef {
diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 137dcf5cf4..7586e0538a 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2728,7 +2728,8 @@ qemuProcessSetupPid(virDomainObj *vm,
     /* Set scheduler type and priority, but not for the main thread. */
     if (sched &&
         nameval != VIR_CGROUP_THREAD_EMULATOR &&
-        virProcessSetScheduler(pid, sched->policy, sched->priority) < 0)
+        virProcessSetScheduler(pid, sched->policy, sched->priority,
+                               sched->runtime, sched->deadline, sched->period) < 0)
         goto cleanup;
 
     ret = 0;
@@ -7813,7 +7814,10 @@ qemuProcessLaunch(virConnectPtr conn,
     if (vm->def->cputune.emulatorsched &&
         virProcessSetScheduler(vm->pid,
                                vm->def->cputune.emulatorsched->policy,
-                               vm->def->cputune.emulatorsched->priority) < 0)
+                               vm->def->cputune.emulatorsched->priority,
+                               vm->def->cputune.emulatorsched->runtime,
+                               vm->def->cputune.emulatorsched->deadline,
+                               vm->def->cputune.emulatorsched->period) < 0)
         goto cleanup;
 
     VIR_DEBUG("Setting any required VM passwords");
diff --git a/src/util/virprocess.c b/src/util/virprocess.c
index a8f86784e1..c96bfc45fd 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -84,6 +84,7 @@ VIR_ENUM_IMPL(virProcessSchedPolicy,
               "idle",
               "fifo",
               "rr",
+              "deadline",
 );
 
 
@@ -1610,6 +1611,13 @@ virProcessSchedTranslatePolicy(virProcessSchedPolicy policy)
     case VIR_PROC_POLICY_RR:
         return SCHED_RR;
 
+    case VIR_PROC_POLICY_DEADLINE:
+# ifdef SCHED_DEADLINE
+        return SCHED_DEADLINE;
+# else
+        return -1;
+# endif
+
     case VIR_PROC_POLICY_LAST:
         /* nada */
         break;
@@ -1621,13 +1629,20 @@ virProcessSchedTranslatePolicy(virProcessSchedPolicy policy)
 int
 virProcessSetScheduler(pid_t pid,
                        virProcessSchedPolicy policy,
-                       int priority)
+                       int priority,
+                       uint64_t runtime G_GNUC_UNUSED,
+                       uint64_t deadline G_GNUC_UNUSED,
+                       uint64_t period G_GNUC_UNUSED)
 {
     struct sched_param param = {0};
     int pol = virProcessSchedTranslatePolicy(policy);
 
-    VIR_DEBUG("pid=%lld, policy=%d, priority=%u",
-              (long long) pid, policy, priority);
+    VIR_DEBUG("pid=%lld, policy=%d, priority=%u, "
+              "runtime=%llu, deadline=%llu, period=%llu",
+              (long long) pid, policy, priority,
+              (unsigned long long) runtime,
+              (unsigned long long) deadline,
+              (unsigned long long) period);
 
     if (!policy)
         return 0;
@@ -1667,6 +1682,69 @@ virProcessSetScheduler(pid_t pid,
         param.sched_priority = priority;
     }
 
+# ifdef SCHED_DEADLINE
+    if (pol == SCHED_DEADLINE) {
+        struct sched_attr attr = {0};
+        /*
+         * The range is enforced in the kernel.
+         * See: https://man7.org/linux/man-pages/man7/sched.7.html
+         */
+        uint64_t min_value = 1024;
+        uint64_t max_value = (1ULL << 63) - 1;
+
+        if (runtime < min_value || runtime > max_value) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Scheduler runtime %llu out of range "
+                             "[%llu, %llu]"),
+                           (unsigned long long) runtime,
+                           (unsigned long long) min_value,
+                           (unsigned long long) max_value);
+            return -1;
+        }
+
+        if (deadline < runtime || deadline > max_value) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Scheduler deadline %llu out of range "
+                             "[%llu, %llu]"),
+                           (unsigned long long) deadline,
+                           (unsigned long long) runtime,
+                           (unsigned long long) max_value);
+            return -1;
+        }
+
+        if ((period < deadline || period > max_value) && period != 0) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Invalid scheduler period %llu, "
+                             "possible correct values are 0 "
+                             "or [%llu, %llu]"),
+                           (unsigned long long) period,
+                           (unsigned long long) deadline,
+                           (unsigned long long) max_value);
+            return -1;
+        }
+
+        attr.size = sizeof(attr);
+        attr.sched_policy = pol;
+        /*
+         * Setting reset-on-fork is necessary as SCHED_DEADLINE
+         * tasks cannot fork. See:
+         * https://docs.kernel.org/scheduler/sched-deadline.html#default-behavior
+         */
+        attr.sched_flags = SCHED_FLAG_RESET_ON_FORK;
+        attr.sched_runtime = runtime;
+        attr.sched_deadline = deadline;
+        attr.sched_period = period;
+
+        if (sched_setattr(pid, &attr, 0) == 0) {
+            return 0;
+        } else {
+            virReportSystemError(errno,
+                                 _("Cannot set scheduler parameters for pid %lld"),
+                                 (long long) pid);
+            return -1;
+        }
+    }
+# endif
     if (sched_setscheduler(pid, pol, &param) < 0) {
         virReportSystemError(errno,
                              _("Cannot set scheduler parameters for pid %lld"),
diff --git a/src/util/virprocess.h b/src/util/virprocess.h
index 30b6981c73..84fdf00fdf 100644
--- a/src/util/virprocess.h
+++ b/src/util/virprocess.h
@@ -33,6 +33,7 @@ typedef enum {
     VIR_PROC_POLICY_IDLE,
     VIR_PROC_POLICY_FIFO,
     VIR_PROC_POLICY_RR,
+    VIR_PROC_POLICY_DEADLINE,
 
     VIR_PROC_POLICY_LAST
 } virProcessSchedPolicy;
@@ -116,7 +117,10 @@ int virProcessSetupPrivateMountNS(void);
 
 int virProcessSetScheduler(pid_t pid,
                            virProcessSchedPolicy policy,
-                           int priority);
+                           int priority,
+                           uint64_t runtime,
+                           uint64_t deadline,
+                           uint64_t period);
 
 GStrv virProcessGetStat(pid_t pid, pid_t tid);
 
-- 
2.37.1


-- 
------------------------


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