[Xen-devel] [PATCH] xen: schedule: allow dom0 vCPUs to be re-pinned when dom0_vcpus_pin is set

[Matt Wilson <msw@xxxxxxxxxx>]

An administrator may want Xen to pin dom0 vCPUs to pCPUs 1:1 at boot,
but still have the flexibility to change the configuration later.
There's no logic that keys off of domain->is_pinned outside of
sched_init_vcpu() and vcpu_set_affinity(). By adjusting the
is_pinned_vcpu() macro to only check for a single CPU set in the
cpu_affinity mask, dom0 vCPUs can safely be re-pinned after the system
boots.

Signed-off-by: Matt Wilson <msw@xxxxxxxxxx>

diff -r 29247e44df47 -r 2614dd8be3a0 docs/misc/xen-command-line.markdown
--- a/docs/misc/xen-command-line.markdown       Fri Nov 30 21:51:17 2012 +0000
+++ b/docs/misc/xen-command-line.markdown       Wed Dec 05 05:48:23 2012 +0000
@@ -453,7 +453,7 @@ Practices](http://wiki.xen.org/wiki/Xen_
 
 > Default: `false`
 
-Pin dom0 vcpus to their respective pcpus
+Initially pin dom0 vcpus to their respective pcpus
 
 ### e820-mtrr-clip
 > `= <boolean>`
diff -r 29247e44df47 -r 2614dd8be3a0 xen/common/domain.c
--- a/xen/common/domain.c       Fri Nov 30 21:51:17 2012 +0000
+++ b/xen/common/domain.c       Wed Dec 05 05:48:23 2012 +0000
@@ -45,10 +45,6 @@
 /* xen_processor_pmbits: xen control Cx, Px, ... */
 unsigned int xen_processor_pmbits = XEN_PROCESSOR_PM_PX;
 
-/* opt_dom0_vcpus_pin: If true, dom0 VCPUs are pinned. */
-bool_t opt_dom0_vcpus_pin;
-boolean_param("dom0_vcpus_pin", opt_dom0_vcpus_pin);
-
 /* Protect updates/reads (resp.) of domain_list and domain_hash. */
 DEFINE_SPINLOCK(domlist_update_lock);
 DEFINE_RCU_READ_LOCK(domlist_read_lock);
@@ -235,7 +231,6 @@ struct domain *domain_create(
 
     if ( domid == 0 )
     {
-        d->is_pinned = opt_dom0_vcpus_pin;
         d->disable_migrate = 1;
     }
 
diff -r 29247e44df47 -r 2614dd8be3a0 xen/common/schedule.c
--- a/xen/common/schedule.c     Fri Nov 30 21:51:17 2012 +0000
+++ b/xen/common/schedule.c     Wed Dec 05 05:48:23 2012 +0000
@@ -52,6 +52,11 @@ boolean_param("sched_smt_power_savings",
  * */
 int sched_ratelimit_us = SCHED_DEFAULT_RATELIMIT_US;
 integer_param("sched_ratelimit_us", sched_ratelimit_us);
+
+/* opt_dom0_vcpus_pin: If true, dom0 VCPUs are pinned at boot. */
+bool_t opt_dom0_vcpus_pin;
+boolean_param("dom0_vcpus_pin", opt_dom0_vcpus_pin);
+
 /* Various timer handlers. */
 static void s_timer_fn(void *unused);
 static void vcpu_periodic_timer_fn(void *data);
@@ -194,7 +199,8 @@ int sched_init_vcpu(struct vcpu *v, unsi
      * domain-0 VCPUs, are pinned onto their respective physical CPUs.
      */
     v->processor = processor;
-    if ( is_idle_domain(d) || d->is_pinned )
+
+    if ( is_idle_domain(d) || (d->domain_id == 0 && opt_dom0_vcpus_pin) )
         cpumask_copy(v->cpu_affinity, cpumask_of(processor));
     else
         cpumask_setall(v->cpu_affinity);
@@ -595,8 +601,6 @@ int vcpu_set_affinity(struct vcpu *v, co
     cpumask_t online_affinity;
     cpumask_t *online;
 
-    if ( v->domain->is_pinned )
-        return -EINVAL;
     online = VCPU2ONLINE(v);
     cpumask_and(&online_affinity, affinity, online);
     if ( cpumask_empty(&online_affinity) )
diff -r 29247e44df47 -r 2614dd8be3a0 xen/include/xen/sched.h
--- a/xen/include/xen/sched.h   Fri Nov 30 21:51:17 2012 +0000
+++ b/xen/include/xen/sched.h   Wed Dec 05 05:48:23 2012 +0000
@@ -292,8 +292,6 @@ struct domain
     enum { DOMDYING_alive, DOMDYING_dying, DOMDYING_dead } is_dying;
     /* Domain is paused by controller software? */
     bool_t           is_paused_by_controller;
-    /* Domain's VCPUs are pinned 1:1 to physical CPUs? */
-    bool_t           is_pinned;
 
     /* Are any VCPUs polling event channels (SCHEDOP_poll)? */
 #if MAX_VIRT_CPUS <= BITS_PER_LONG
@@ -713,8 +711,7 @@ void watchdog_domain_destroy(struct doma
 
 #define is_hvm_domain(d) ((d)->is_hvm)
 #define is_hvm_vcpu(v)   (is_hvm_domain(v->domain))
-#define is_pinned_vcpu(v) ((v)->domain->is_pinned || \
-                           cpumask_weight((v)->cpu_affinity) == 1)
+#define is_pinned_vcpu(v) (cpumask_weight((v)->cpu_affinity) == 1)
 #ifdef HAS_PASSTHROUGH
 #define need_iommu(d)    ((d)->need_iommu)
 #else

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