[libvirt] [PATCH] Fix QEMU cpu affinity at startup to include all threads

["Daniel P. Berrange" <berrange@xxxxxxxxxx>]

The QEMU cpu affinity is used in NUMA scenarios to ensure that
guest memory is allocated from a specific node. Normally memory
is allocate on demand in vCPU threads, but when using hugepages
the initial thread leader allocates memory upfront. libvirt was
not setting affinity of the thread leader, or I/O threads. This
patch changes the code to set the process affinity in between
the fork()/exec() of QEMU. This ensures that every single QEMU
thread gets the affinity

* src/qemu/qemu_driver.c: Set affinity on entire QEMU process
  at startup
---
 src/qemu/qemu_driver.c |   29 ++++++++++++++++-------------
 1 files changed, 16 insertions(+), 13 deletions(-)

diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
index 257f914..2598deb 100644
--- a/src/qemu/qemu_driver.c
+++ b/src/qemu/qemu_driver.c
@@ -1701,6 +1701,9 @@ qemuDetectVcpuPIDs(struct qemud_driver *driver,
     return 0;
 }
 
+/*
+ * To be run between fork/exec of QEMU only
+ */
 static int
 qemudInitCpuAffinity(virDomainObjPtr vm)
 {
@@ -1708,7 +1711,8 @@ qemudInitCpuAffinity(virDomainObjPtr vm)
     virNodeInfo nodeinfo;
     unsigned char *cpumap;
     int cpumaplen;
-    qemuDomainObjPrivatePtr priv = vm->privateData;
+
+    DEBUG0("Setting CPU affinity");
 
     if (nodeGetInfo(NULL, &nodeinfo) < 0)
         return -1;
@@ -1740,14 +1744,14 @@ qemudInitCpuAffinity(virDomainObjPtr vm)
             VIR_USE_CPU(cpumap, i);
     }
 
-    /* The XML config only gives a per-VM affinity, so we apply
-     * the same mapping to all vCPUs */
-    for (i = 0 ; i < priv->nvcpupids ; i++) {
-        if (virProcessInfoSetAffinity(priv->vcpupids[i],
-                                      cpumap, cpumaplen, maxcpu) < 0) {
-            VIR_FREE(cpumap);
-            return -1;
-        }
+    /* We are assuming we are running between fork/exec of QEMU, so
+     * that getpid() gives the QEMU process ID and we know that
+     * no threads are running.
+     */
+    if (virProcessInfoSetAffinity(getpid(),
+                                  cpumap, cpumaplen, maxcpu) < 0) {
+        VIR_FREE(cpumap);
+        return -1;
     }
     VIR_FREE(cpumap);
 
@@ -2653,6 +2657,9 @@ struct qemudHookData {
 static int qemudSecurityHook(void *data) {
     struct qemudHookData *h = data;
 
+    if (qemudInitCpuAffinity(h->vm) < 0)
+        return -1;
+
     if (qemuAddToCgroup(h->driver, h->vm->def) < 0)
         return -1;
 
@@ -2943,10 +2950,6 @@ static int qemudStartVMDaemon(virConnectPtr conn,
     if (qemuDetectVcpuPIDs(driver, vm) < 0)
         goto abort;
 
-    DEBUG0("Setting CPU affinity");
-    if (qemudInitCpuAffinity(vm) < 0)
-        goto abort;
-
     DEBUG0("Setting any required VM passwords");
     if (qemuInitPasswords(conn, driver, vm, qemuCmdFlags) < 0)
         goto abort;
-- 
1.6.2.5

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