[libvirt] [PATCH 2/6] util: allow virProcessSetScheduler to set SCHED_DEADLINE

[Martin Polednik]

As sched_deadline is linux specific, it is not set through
sched_setscheduler but rather the sched_setattr syscall. Additionally,
the scheduler has new set of parameters: runtime, deadline and period.

In this part of the series, we extend virProcessSetScheduler to
accommodate the additional parameters and use sched_setattr syscall to
set SCHED_DEADLINE. Another small addition is sched_attr struct, which
is required for sched_setattr and not exposed from the kernel or
libraries.
---
 src/qemu/qemu_process.c |  3 ++-
 src/util/virprocess.c   | 70 +++++++++++++++++++++++++++++++++++++++++++++++--
 src/util/virprocess.h   | 28 +++++++++++++++++++-
 3 files changed, 97 insertions(+), 4 deletions(-)

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 1b67aee..91a635c 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -2395,7 +2395,8 @@ qemuProcessSetupPid(virDomainObjPtr vm,
 
     /* Set scheduler type and priority. */
     if (sched &&
-        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/util/virprocess.c b/src/util/virprocess.c
index d68800b..cd1cc9b 100644
--- a/src/util/virprocess.c
+++ b/src/util/virprocess.c
@@ -70,6 +70,7 @@
 VIR_LOG_INIT("util.process");
 
 #ifdef __linux__
+# include <sys/syscall.h>
 /*
  * Workaround older glibc. While kernel may support the setns
  * syscall, the glibc wrapper might not exist. If that's the
@@ -91,9 +92,14 @@ VIR_LOG_INIT("util.process");
 #  endif
 # endif
 
+# ifndef __NR_sched_setattr
+#  if defined(__x86_64__)
+#   define __NR_sched_setattr 314
+#  endif
+# endif
+
 # ifndef HAVE_SETNS
 #  if defined(__NR_setns)
-#   include <sys/syscall.h>
 
 static inline int setns(int fd, int nstype)
 {
@@ -103,6 +109,13 @@ static inline int setns(int fd, int nstype)
 #   error Please determine the syscall number for setns on your architecture
 #  endif
 # endif
+
+static inline int sched_setattr(pid_t pid,
+                                const struct sched_attr *attr,
+                                unsigned int flags)
+{
+    return syscall(__NR_sched_setattr, pid, attr, flags);
+}
 #else /* !__linux__ */
 static inline int setns(int fd ATTRIBUTE_UNUSED, int nstype ATTRIBUTE_UNUSED)
 {
@@ -110,6 +123,15 @@ static inline int setns(int fd ATTRIBUTE_UNUSED, int nstype ATTRIBUTE_UNUSED)
                          _("Namespaces are not supported on this platform."));
     return -1;
 }
+
+static inline int sched_setattr(pid_t pid,
+                                const struct sched_attr *attr,
+                                unsigned int flags)
+{
+    virReportSystemError(ENOSYS, "%s",
+                         _("Deadline scheduler is not supported on this platform."));
+    return -1;
+}
 #endif
 
 VIR_ENUM_IMPL(virProcessSchedPolicy, VIR_PROC_POLICY_LAST,
@@ -1225,7 +1247,10 @@ virProcessSchedTranslatePolicy(virProcessSchedPolicy policy)
 int
 virProcessSetScheduler(pid_t pid,
                        virProcessSchedPolicy policy,
-                       int priority)
+                       int priority,
+                       unsigned long long runtime,
+                       unsigned long long deadline,
+                       unsigned long long period)
 {
     struct sched_param param = {0};
     int pol = virProcessSchedTranslatePolicy(policy);
@@ -1235,6 +1260,47 @@ virProcessSetScheduler(pid_t pid,
     if (!policy)
         return 0;
 
+    if (pol == SCHED_DEADLINE) {
+        int ret = 0;
+
+        if (runtime < 1024 || deadline < 1024 || period < 24) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                        _("Scheduler runtime, deadline and period must be "
+                          "higher or equal to 1024 (1 us) (runtime(%llu), "
+                          "deadline(%llu), period(%llu))"), runtime, deadline, period);
+            return -1;
+        }
+
+        if (!(runtime <= deadline && deadline <= period)) {
+            virReportError(VIR_ERR_CONFIG_UNSUPPORTED,
+                           _("Scheduler configuration does not satisfy "
+                             "(runtime(%llu) <= deadline(%llu) <= period(%llu))"),
+                           runtime, deadline, period);
+            return -1;
+        }
+
+        struct sched_attr attrs = {
+           .size = sizeof(attrs),
+           .sched_policy = SCHED_DEADLINE,
+           .sched_flags = 0,
+           .sched_nice = 0,
+           .sched_priority = 0,
+           .sched_runtime = runtime,
+           .sched_deadline = deadline,
+           .sched_period = period,
+        };
+
+        ret = sched_setattr(pid, &attrs, 0);
+        if (ret != 0) {
+            virReportSystemError(errno,
+                                 _("Cannot set scheduler parameters for pid %d"),
+                                 pid);
+            return -1;
+        }
+
+        return 0;
+    }
+
     if (pol == SCHED_FIFO || pol == SCHED_RR) {
         int min = 0;
         int max = 0;
diff --git a/src/util/virprocess.h b/src/util/virprocess.h
index 1eac3e6..e6914e7 100644
--- a/src/util/virprocess.h
+++ b/src/util/virprocess.h
@@ -23,6 +23,9 @@
 # define __VIR_PROCESS_H__
 
 # include <sys/types.h>
+# ifdef __linux__
+#  include <linux/types.h>
+# endif
 
 # include "internal.h"
 # include "virbitmap.h"
@@ -39,6 +42,26 @@ typedef enum {
     VIR_PROC_POLICY_LAST
 } virProcessSchedPolicy;
 
+# ifdef __linux__
+struct sched_attr {
+    __u32 size;
+
+    __u32 sched_policy;
+    __u64 sched_flags;
+
+    /* SCHED_NORMAL, SCHED_BATCH */
+    __s32 sched_nice;
+
+    /* SCHED_FIFO, SCHED_RR */
+    __u32 sched_priority;
+
+    /* SCHED_DEADLINE (nsec) */
+    __u64 sched_runtime;
+    __u64 sched_deadline;
+    __u64 sched_period;
+};
+# endif
+
 VIR_ENUM_DECL(virProcessSchedPolicy);
 
 char *
@@ -93,6 +116,9 @@ int virProcessRunInMountNamespace(pid_t pid,
 
 int virProcessSetScheduler(pid_t pid,
                            virProcessSchedPolicy policy,
-                           int priority);
+                           int priority,
+                           unsigned long long runtime,
+                           unsigned long long deadline,
+                           unsigned long long period);
 
 #endif /* __VIR_PROCESS_H__ */
-- 
2.8.1