[Xen-devel] [PATCH 49/60] xen/sched: reject switching smt on/off with core scheduling active

[Juergen Gross <jgross@xxxxxxxx>]

When core or socket scheduling are active enabling or disabling smt is
not possible as that would require a major host reconfiguration.

Add a bool sched_disable_smt_switching which will be set for core or
socket scheduling.

Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
---
V1: new patch
---
 xen/arch/x86/sysctl.c   | 3 ++-
 xen/common/schedule.c   | 1 +
 xen/include/xen/sched.h | 1 +
 3 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/xen/arch/x86/sysctl.c b/xen/arch/x86/sysctl.c
index 3f06fecbd8..034d78fe67 100644
--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -200,7 +200,8 @@ long arch_do_sysctl(
 
         case XEN_SYSCTL_CPU_HOTPLUG_SMT_ENABLE:
         case XEN_SYSCTL_CPU_HOTPLUG_SMT_DISABLE:
-            if ( !cpu_has_htt || boot_cpu_data.x86_num_siblings < 2 )
+            if ( !cpu_has_htt || boot_cpu_data.x86_num_siblings < 2 ||
+                 sched_disable_smt_switching )
             {
                 ret = -EOPNOTSUPP;
                 break;
diff --git a/xen/common/schedule.c b/xen/common/schedule.c
index 3c85861b15..8607262a71 100644
--- a/xen/common/schedule.c
+++ b/xen/common/schedule.c
@@ -57,6 +57,7 @@ integer_param("sched_ratelimit_us", sched_ratelimit_us);
 
 /* Number of vcpus per struct sched_unit. */
 static unsigned int sched_granularity = 1;
+bool sched_disable_smt_switching;
 const cpumask_t *sched_res_mask = &cpumask_all;
 
 /* Various timer handlers. */
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index b6496f57f6..7dc63c449b 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -1020,6 +1020,7 @@ static inline bool is_vcpu_online(const struct vcpu *v)
 }
 
 extern bool sched_smt_power_savings;
+extern bool sched_disable_smt_switching;
 
 extern enum cpufreq_controller {
     FREQCTL_none, FREQCTL_dom0_kernel, FREQCTL_xen
-- 
2.16.4


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