Hi,
This patch allows a domain's vcpus to increase beyond the max (up to
CONFIG_NR_CPUS) set at creation time by making 3 changes:
1. xen/common/dom0_ops.c - removes the check in DOM0_MAX_CPUS that
doesnt allow vcpus to be alloc'd after the first vcpu has been
initialiazed.
2. xend/XendDomainInfo.py - when vcpu-set is given a value greater than
the current vcpu count, the dom0_op above is called with the new value
and the store is updated.
3. drivers/xen/core/smpboot.c - the cpu_possible_map and
cpu_present_map made to reflect the values outlined in
include/linux/cpumask.h when CONFIG_HOTPLUG_CPU is set:
cpu_possible_map - all NR_CPUS bits set
cpu_present_map - has bit 'cpu' set iff cpu is populated
cpu_online_map - has bit 'cpu' set iff cpu available to
scheduler
This has been tested on x86_32 and x86_64 with and without
CONFIG_HOTPLUG_CPU.
Does anyone know what potential races are being avoided by the check in
dom0_ops.c that this patch removes?
Any comments on the patch?
Thanks,
Ryan
Signed-off-by: Ryan Grimm <grimm@xxxxxxxxxx>
diff -r 1346a69694be -r 334b38a81c7d
linux-2.6-xen-sparse/drivers/xen/core/smpboot.c
--- a/linux-2.6-xen-sparse/drivers/xen/core/smpboot.c Wed Feb 15 14:20:32 2006
+++ b/linux-2.6-xen-sparse/drivers/xen/core/smpboot.c Wed Feb 15 11:54:51 2006
@@ -57,6 +57,7 @@
#ifdef CONFIG_HOTPLUG_CPU
DEFINE_PER_CPU(int, cpu_state) = { 0 };
+static int vcpu_allocated(unsigned int vcpu);
#endif
static DEFINE_PER_CPU(int, resched_irq);
@@ -81,15 +82,17 @@
void __init prefill_possible_map(void)
{
- int i, rc;
+ int i;
if (!cpus_empty(cpu_possible_map))
return;
for (i = 0; i < NR_CPUS; i++) {
- rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
+#ifndef CONFIG_HOTPLUG_CPU
+ int rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, i, NULL);
if (rc == -ENOENT)
break;
+#endif
cpu_set(i, cpu_possible_map);
}
}
@@ -257,11 +260,15 @@
#ifdef CONFIG_HOTPLUG_CPU
if (xen_start_info->flags & SIF_INITDOMAIN)
cpu_set(cpu, cpu_present_map);
+ if (vcpu_allocated(cpu)) {
+ vcpu_prepare(cpu);
+ cpu_set(cpu, cpu_present_map);
+ }
#else
cpu_set(cpu, cpu_present_map);
-#endif
-
vcpu_prepare(cpu);
+#endif
+
}
/* Currently, Xen gives no dynamic NUMA/HT info. */
@@ -289,17 +296,15 @@
#ifdef CONFIG_HOTPLUG_CPU
-/*
- * Initialize cpu_present_map late to skip SMP boot code in init/main.c.
- * But do it early enough to catch critical for_each_present_cpu() loops
- * in i386-specific code.
- */
-static int __init initialize_cpu_present_map(void)
-{
- cpu_present_map = cpu_possible_map;
- return 0;
-}
-core_initcall(initialize_cpu_present_map);
+static int vcpu_allocated(unsigned int vcpu)
+{
+ int rc = HYPERVISOR_vcpu_op(VCPUOP_is_up, vcpu, NULL);
+ if (rc >= 0)
+ rc = 1;
+ else
+ rc = 0;
+ return rc;
+}
static void vcpu_hotplug(unsigned int cpu)
{
@@ -312,11 +317,17 @@
sprintf(dir, "cpu/%d", cpu);
err = xenbus_scanf(XBT_NULL, dir, "availability", "%s", state);
if (err != 1) {
- printk(KERN_ERR "XENBUS: Unable to read cpu state\n");
+ printk(KERN_ERR "XENBUS: Unable to read cpu %d state\n", cpu);
return;
}
if (strcmp(state, "online") == 0) {
+ if (!vcpu_allocated(cpu))
+ return;
+ if (!cpu_present(cpu)) {
+ vcpu_prepare(cpu);
+ cpu_set(cpu, cpu_present_map);
+ }
(void)cpu_up(cpu);
} else if (strcmp(state, "offline") == 0) {
(void)cpu_down(cpu);
diff -r 1346a69694be -r 334b38a81c7d tools/python/xen/xend/XendDomainInfo.py
--- a/tools/python/xen/xend/XendDomainInfo.py Wed Feb 15 14:20:32 2006
+++ b/tools/python/xen/xend/XendDomainInfo.py Wed Feb 15 11:54:51 2006
@@ -750,6 +750,9 @@
def setVCpuCount(self, vcpus):
+ if vcpus > self.getVCpuCount():
+ xc.domain_max_vcpus(self.domid, vcpus)
+ self.info['vcpus'] = vcpus
self.info['vcpu_avail'] = (1 << vcpus) - 1
self.storeVm('vcpu_avail', self.info['vcpu_avail'])
self.writeDom(self.vcpuDomDetails())
diff -r 1346a69694be -r 334b38a81c7d xen/common/dom0_ops.c
--- a/xen/common/dom0_ops.c Wed Feb 15 14:20:32 2006
+++ b/xen/common/dom0_ops.c Wed Feb 15 11:54:51 2006
@@ -236,15 +236,6 @@
if ( (d = find_domain_by_id(op->u.max_vcpus.domain)) == NULL )
break;
- /*
- * Can only create new VCPUs while the domain is not fully constructed
- * (and hence not runnable). Xen needs auditing for races before
- * removing this check.
- */
- ret = -EINVAL;
- if ( test_bit(_VCPUF_initialised, &d->vcpu[0]->vcpu_flags) )
- goto maxvcpu_out;
-
/* We cannot reduce maximum VCPUs. */
ret = -EINVAL;
if ( (max != MAX_VIRT_CPUS) && (d->vcpu[max] != NULL) )
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