qemu: Don't try to 'fix up' cpuset.mems after QEMU's memory allocation

In ideal world, my plan was perfect. We allow union of all host
nodes in cpuset.mems and once QEMU has allocated its memory, we
'fix up' restriction of its emulator thread by writing the
original value we wanted to set all along. But in fact, we can't
do it because that triggers memory movement. For instance,
consider the following <numatune/>:

  <numatune>
    <memory mode="strict" nodeset="0"/>
    <memnode cellid="1" mode="strict" nodeset="1"/>
  </numatune>

  <numa>
    <cell id="0" cpus="0-1" memory="1024000" unit="KiB" />
    <cell id="1" cpus="2-3" memory="1048576" unit="KiB"/>
  </numa>

This is meant to create 1:1 mapping between guest and host NUMA
nodes. So we start QEMU with cpuset.mems set to "0-1" (so that it
can allocate memory even for guest node #1 and have the memory
come fro host node #1) and then, set cpuset.mems to "0" (because
that's where we wanted emulator thread to live).

But this in turn triggers movement of all memory (even the
allocated one) to host NUMA node #0. Therefore, we have to just
keep cpuset.mems untouched and rely on .host-nodes passed on the
QEMU cmd line.

The placement still suffers because of cpuset.mems set for vcpus
or iothreads, but that's fixed in next commit.

Fixes: 3ec6d586bc
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Martin Kletzander <mkletzan@redhat.com>

src/qemu/qemu_hotplug.c

@@ -2295,7 +2295,7 @@ qemuDomainAttachMemory(virQEMUDriver *driver,
     if (qemuDomainAdjustMaxMemLock(vm) < 0)
         goto removedef;
 
-    if (qemuProcessSetupEmulator(vm, true) < 0)
+    if (qemuProcessSetupEmulator(vm) < 0)
         goto removedef;
     restoreemulatorcgroup = true;
 
@@ -2336,11 +2336,10 @@ qemuDomainAttachMemory(virQEMUDriver *driver,
             VIR_WARN("Unable to remove memory device from /dev");
         if (releaseaddr)
             qemuDomainReleaseMemoryDeviceSlot(vm, mem);
+        if (restoreemulatorcgroup)
+            qemuProcessSetupEmulator(vm);
     }
 
-    if (restoreemulatorcgroup)
-        qemuProcessSetupEmulator(vm, false);
-
     virDomainMemoryDefFree(mem);
     return ret;
 

src/qemu/qemu_process.c

@@ -2596,9 +2596,7 @@ qemuProcessSetupPid(virDomainObj *vm,
              mem_mode == VIR_DOMAIN_NUMATUNE_MEM_RESTRICTIVE)) {
 
             /* QEMU allocates its memory from the emulator thread. Thus it
-             * needs to access union of all host nodes configured. This is
-             * going to be replaced with proper value later in the startup
-             * process. */
+             * needs to access union of all host nodes configured. */
             if (unionMems &&
                 nameval == VIR_CGROUP_THREAD_EMULATOR &&
                 mem_mode != VIR_DOMAIN_NUMATUNE_MEM_RESTRICTIVE) {
@@ -2702,15 +2700,14 @@ qemuProcessSetupPid(virDomainObj *vm,
 
 
 int
-qemuProcessSetupEmulator(virDomainObj *vm,
-                         bool unionMems)
+qemuProcessSetupEmulator(virDomainObj *vm)
 {
     return qemuProcessSetupPid(vm, vm->pid, VIR_CGROUP_THREAD_EMULATOR,
                                0, vm->def->cputune.emulatorpin,
                                vm->def->cputune.emulator_period,
                                vm->def->cputune.emulator_quota,
                                vm->def->cputune.emulatorsched,
-                               unionMems);
+                               true);
 }
 
 
@@ -7764,7 +7761,7 @@ qemuProcessLaunch(virConnectPtr conn,
         goto cleanup;
 
     VIR_DEBUG("Setting emulator tuning/settings");
-    if (qemuProcessSetupEmulator(vm, true) < 0)
+    if (qemuProcessSetupEmulator(vm) < 0)
         goto cleanup;
 
     VIR_DEBUG("Setting cgroup for external devices (if required)");
@@ -7827,10 +7824,6 @@ qemuProcessLaunch(virConnectPtr conn,
     if (qemuConnectAgent(driver, vm) < 0)
         goto cleanup;
 
-    VIR_DEBUG("Fixing up emulator tuning/settings");
-    if (qemuProcessSetupEmulator(vm, false) < 0)
-        goto cleanup;
-
     VIR_DEBUG("setting up hotpluggable cpus");
     if (qemuDomainHasHotpluggableStartupVcpus(vm->def)) {
         if (qemuDomainRefreshVcpuInfo(vm, asyncJob, false) < 0)

src/qemu/qemu_process.h

@@ -236,5 +236,4 @@ void qemuProcessCleanupMigrationJob(virQEMUDriver *driver,
 void qemuProcessRefreshDiskProps(virDomainDiskDef *disk,
                                  struct qemuDomainDiskInfo *info);
 
-int qemuProcessSetupEmulator(virDomainObj *vm,
-                             bool unionMems);
+int qemuProcessSetupEmulator(virDomainObj *vm);