From d94242248232c8c47bf96d1b7a480f36332ae0db Mon Sep 17 00:00:00 2001
From: Michal Privoznik <mprivozn@redhat.com>
Date: Thu, 11 Aug 2022 15:25:24 +0200
Subject: [PATCH] qemu: Enable SCHED_CORE for vCPUs
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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>
---
 src/qemu/qemu_process.c | 39 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 39 insertions(+)

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;
 }
 
-- 
2.47.2