qemu: Keep the affinity when creating cgroup for emulator thread

When the cpu placement model is "auto", it sets the affinity for
domain process with the advisory nodeset from numad, however,
creating cgroup for the domain process (called emulator thread
in some contexts) later overrides that with pinning it to all
available pCPUs.

How to reproduce:

  * Configure the domain with "auto" placement for <vcpu>, e.g.
    <vcpu placement='auto'>4</vcpu>
  * % virsh start dom
  * % cat /proc/$dompid/status

Though the emulator cgroup cause conflicts, but we can't simply
prohibit creating it, as other tunables are still useful, such
as "emulator_period", which is used by API
virDomainSetSchedulerParameter. So this patch doesn't prohibit
creating the emulator cgroup, but inherit the nodeset from numad,
and reset the affinity for domain process.

* src/qemu/qemu_cgroup.h: Modify definition of qemuSetupCgroupForEmulator
                          to accept the passed nodenet
* src/qemu/qemu_cgroup.c: Set the affinity with the passed nodeset

src/qemu/qemu_cgroup.c

@@ -25,6 +25,7 @@
 
 #include "qemu_cgroup.h"
 #include "qemu_domain.h"
+#include "qemu_process.h"
 #include "cgroup.h"
 #include "logging.h"
 #include "memory.h"
@@ -637,9 +638,11 @@ cleanup:
 }
 
 int qemuSetupCgroupForEmulator(struct qemud_driver *driver,
-                               virDomainObjPtr vm)
+                               virDomainObjPtr vm,
+                               virBitmapPtr nodemask)
 {
     virBitmapPtr cpumask = NULL;
+    virBitmapPtr cpumap = NULL;
     virCgroupPtr cgroup = NULL;
     virCgroupPtr cgroup_emulator = NULL;
     virDomainDefPtr def = vm->def;
@@ -687,10 +690,15 @@ int qemuSetupCgroupForEmulator(struct qemud_driver *driver,
         }
     }
 
-    if (def->cputune.emulatorpin)
+    if (def->placement_mode == VIR_DOMAIN_CPU_PLACEMENT_MODE_AUTO) {
+        if (!(cpumap = qemuPrepareCpumap(driver, nodemask)))
+            goto cleanup;
+        cpumask = cpumap;
+    } else if (def->cputune.emulatorpin) {
         cpumask = def->cputune.emulatorpin->cpumask;
-    else if (def->cpumask)
+    } else if (def->cpumask) {
         cpumask = def->cpumask;
+    }
 
     if (cpumask) {
         if (qemuCgroupControllerActive(driver, VIR_CGROUP_CONTROLLER_CPUSET)) {
@@ -711,9 +719,12 @@ int qemuSetupCgroupForEmulator(struct qemud_driver *driver,
 
     virCgroupFree(&cgroup_emulator);
     virCgroupFree(&cgroup);
+    virBitmapFree(cpumap);
     return 0;
 
 cleanup:
+    virBitmapFree(cpumap);
+
     if (cgroup_emulator) {
         virCgroupRemove(cgroup_emulator);
         virCgroupFree(&cgroup_emulator);

src/qemu/qemu_cgroup.h

@@ -58,7 +58,8 @@ int qemuSetupCgroupVcpuPin(virCgroupPtr cgroup,
 int qemuSetupCgroupEmulatorPin(virCgroupPtr cgroup, virBitmapPtr cpumask);
 int qemuSetupCgroupForVcpu(struct qemud_driver *driver, virDomainObjPtr vm);
 int qemuSetupCgroupForEmulator(struct qemud_driver *driver,
-                               virDomainObjPtr vm);
+                               virDomainObjPtr vm,
+                               virBitmapPtr nodemask);
 int qemuRemoveCgroup(struct qemud_driver *driver,
                      virDomainObjPtr vm,
                      int quiet);

src/qemu/qemu_process.c

@@ -3812,7 +3812,7 @@ int qemuProcessStart(virConnectPtr conn,
         goto cleanup;
 
     VIR_DEBUG("Setting cgroup for emulator (if required)");
-    if (qemuSetupCgroupForEmulator(driver, vm) < 0)
+    if (qemuSetupCgroupForEmulator(driver, vm, nodemask) < 0)
         goto cleanup;
 
     VIR_DEBUG("Setting VCPU affinities");