From: Michal Privoznik <mprivozn@redhat.com>
Date: Thu, 11 Aug 2022 13:25:24 +0000 (+0200)
Subject: qemu: Enable SCHED_CORE for vCPUs
X-Git-Url: http://xenbits.xensource.com/gitweb?a=commitdiff_plain;h=d94242248232c8c47bf96d1b7a480f36332ae0db;p=libvirt.git

qemu: Enable SCHED_CORE for vCPUs

For QEMU_SCHED_CORE_VCPUS case, the vCPU threads should be placed
all into one scheduling group, but not the emulator or any of its
threads. Therefore, as soon as vCPU TIDs are detected, fork off a
child which then creates a separate scheduling group and adds all
vCPU threads into it.

Please note, this commit only handles the cold boot case. Hotplug
is going to be implemented in the next commit.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
---

diff --git a/src/qemu/qemu_process.c b/src/qemu/qemu_process.c
index 5ce181fea7..6395694e7b 100644
--- a/src/qemu/qemu_process.c
+++ b/src/qemu/qemu_process.c
@@ -5854,9 +5854,44 @@ qemuProcessSetupVcpu(virDomainObj *vm,
 }
 
 
+static int
+qemuProcessSetupAllVcpusSchedCoreHelper(pid_t ppid G_GNUC_UNUSED,
+                                        void *opaque)
+{
+    virDomainObj *vm = opaque;
+    size_t i;
+
+    /* Since we are setting all vCPU threads at once and from a forked off
+     * child, we don't need the dummy schedCoreChildPID and can create one on
+     * our own. */
+    if (virProcessSchedCoreCreate() < 0) {
+        virReportSystemError(errno, "%s",
+                             _("Unable to set SCHED_CORE"));
+
+        return -1;
+    }
+
+    for (i = 0; i < virDomainDefGetVcpusMax(vm->def); i++) {
+        pid_t vcpupid = qemuDomainGetVcpuPid(vm, i);
+
+        if (vcpupid > 0 &&
+            virProcessSchedCoreShareTo(vcpupid) < 0) {
+            virReportSystemError(errno,
+                                 _("unable to share scheduling cookie to %lld"),
+                                 (long long) vcpupid);
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+
 static int
 qemuProcessSetupVcpus(virDomainObj *vm)
 {
+    qemuDomainObjPrivate *priv = vm->privateData;
+    g_autoptr(virQEMUDriverConfig) cfg = virQEMUDriverGetConfig(priv->driver);
     virDomainVcpuDef *vcpu;
     unsigned int maxvcpus = virDomainDefGetVcpusMax(vm->def);
     size_t i;
@@ -5899,6 +5934,10 @@ qemuProcessSetupVcpus(virDomainObj *vm)
             return -1;
     }
 
+    if (cfg->schedCore == QEMU_SCHED_CORE_VCPUS &&
+        virProcessRunInFork(qemuProcessSetupAllVcpusSchedCoreHelper, vm) < 0)
+        return -1;
+
     return 0;
 }