[Xen-devel] [PATCH 1/2] core-parking: interact with runtime SMT-disabling

["Jan Beulich" <JBeulich@xxxxxxxx>]

When disabling SMT at runtime, secondary threads should no longer be
candidates for bringing back up in response to _PUD ACPI events. Purge
them from the tracking array.

Doing so involves adding locking to guard accounting data in the core
parking code. While adding the declaration for the lock take the liberty
to drop two unnecessary forward function declarations.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/sysctl.c
+++ b/xen/arch/x86/sysctl.c
@@ -128,6 +128,9 @@ static long smt_up_down_helper(void *dat
         if ( !(x86_cpu_to_apicid[cpu] & sibling_mask) )
             continue;
 
+        if ( !up && core_parking_remove(cpu) )
+            continue;
+
         ret = up ? cpu_up_helper(_p(cpu))
                  : cpu_down_helper(_p(cpu));
 
--- a/xen/common/core_parking.c
+++ b/xen/common/core_parking.c
@@ -25,9 +25,7 @@
 #define CORE_PARKING_INCREMENT 1
 #define CORE_PARKING_DECREMENT 2
 
-static unsigned int core_parking_power(unsigned int event);
-static unsigned int core_parking_performance(unsigned int event);
-
+static DEFINE_SPINLOCK(accounting_lock);
 static uint32_t cur_idle_nums;
 static unsigned int core_parking_cpunum[NR_CPUS] = {[0 ... NR_CPUS-1] = -1};
 
@@ -100,10 +98,10 @@ static unsigned int core_parking_perform
     break;
 
     case CORE_PARKING_DECREMENT:
-    {
-        cpu = core_parking_cpunum[cur_idle_nums -1];
-    }
-    break;
+        spin_lock(&accounting_lock);
+        cpu = core_parking_cpunum[cur_idle_nums - 1];
+        spin_unlock(&accounting_lock);
+        break;
 
     default:
         break;
@@ -158,10 +156,10 @@ static unsigned int core_parking_power(u
     break;
 
     case CORE_PARKING_DECREMENT:
-    {
-        cpu = core_parking_cpunum[cur_idle_nums -1];
-    }
-    break;
+        spin_lock(&accounting_lock);
+        cpu = core_parking_cpunum[cur_idle_nums - 1];
+        spin_unlock(&accounting_lock);
+        break;
 
     default:
         break;
@@ -185,7 +183,11 @@ long core_parking_helper(void *data)
         ret = cpu_down(cpu);
         if ( ret )
             return ret;
+
+        spin_lock(&accounting_lock);
+        BUG_ON(cur_idle_nums >= ARRAY_SIZE(core_parking_cpunum));
         core_parking_cpunum[cur_idle_nums++] = cpu;
+        spin_unlock(&accounting_lock);
     }
 
     while ( cur_idle_nums > idle_nums )
@@ -194,12 +196,43 @@ long core_parking_helper(void *data)
         ret = cpu_up(cpu);
         if ( ret )
             return ret;
-        core_parking_cpunum[--cur_idle_nums] = -1;
+
+        if ( !core_parking_remove(cpu) )
+        {
+            ret = cpu_down(cpu);
+            if ( ret == -EEXIST )
+                ret = 0;
+            if ( ret )
+                break;
+        }
     }
 
     return ret;
 }
 
+bool core_parking_remove(unsigned int cpu)
+{
+    unsigned int i;
+    bool found = false;
+
+    spin_lock(&accounting_lock);
+
+    for ( i = 0; i < cur_idle_nums; ++i )
+        if ( core_parking_cpunum[i] == cpu )
+        {
+            found = true;
+            --cur_idle_nums;
+            break;
+        }
+
+    for ( ; i < cur_idle_nums; ++i )
+        core_parking_cpunum[i] = core_parking_cpunum[i + 1];
+
+    spin_unlock(&accounting_lock);
+
+    return found;
+}
+
 uint32_t get_cur_idle_nums(void)
 {
     return cur_idle_nums;
--- a/xen/include/asm-x86/smp.h
+++ b/xen/include/asm-x86/smp.h
@@ -63,6 +63,7 @@ long cpu_up_helper(void *data);
 long cpu_down_helper(void *data);
 
 long core_parking_helper(void *data);
+bool core_parking_remove(unsigned int cpu);
 uint32_t get_cur_idle_nums(void);
 
 /*





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