powerpc/sched: Cleanup vcpu_is_preempted()

No functional change in this patch. A helper is added to find if
vcpu is dispatched by hypervisor. Use that instead of opencoding.
Also clarify some of the comments.

Signed-off-by: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20231114071219.198222-1-aneesh.kumar@linux.ibm.com

diff --git a/arch/powerpc/include/asm/paravirt.h b/arch/powerpc/include/asm/paravirt.h
index ac4279208d63328ec0797ff22d774b53d9fcac8c..b78b82d660577626adc9ce47ffe449d68a36daa7 100644 (file)
--- a/arch/powerpc/include/asm/paravirt.h
+++ b/arch/powerpc/include/asm/paravirt.h
@@ -76,6 +76,17 @@ static inline bool is_vcpu_idle(int vcpu)
 {
        return lppaca_of(vcpu).idle;
 }
+
+static inline bool vcpu_is_dispatched(int vcpu)
+{
+       /*
+        * This is the yield_count.  An "odd" value (low bit on) means that
+        * the processor is yielded (either because of an OS yield or a
+        * hypervisor preempt).  An even value implies that the processor is
+        * currently executing.
+        */
+       return (!(yield_count_of(vcpu) & 1));
+}
 #else
 static inline bool is_shared_processor(void)
 {
@@ -109,6 +120,10 @@ static inline bool is_vcpu_idle(int vcpu)
 {
        return false;
 }
+static inline bool vcpu_is_dispatched(int vcpu)
+{
+       return true;
+}
 #endif
 
 #define vcpu_is_preempted vcpu_is_preempted
@@ -134,12 +149,12 @@ static inline bool vcpu_is_preempted(int cpu)
         * If the hypervisor has dispatched the target CPU on a physical
         * processor, then the target CPU is definitely not preempted.
         */
-       if (!(yield_count_of(cpu) & 1))
+       if (vcpu_is_dispatched(cpu))
                return false;
 
        /*
-        * If the target CPU has yielded to Hypervisor but OS has not
-        * requested idle then the target CPU is definitely preempted.
+        * if the target CPU is not dispatched and the guest OS
+        * has not marked the CPU idle, then it is hypervisor preempted.
         */
        if (!is_vcpu_idle(cpu))
                return true;
@@ -166,7 +181,7 @@ static inline bool vcpu_is_preempted(int cpu)
 
                /*
                 * The PowerVM hypervisor dispatches VMs on a whole core
-                * basis. So we know that a thread sibling of the local CPU
+                * basis. So we know that a thread sibling of the executing CPU
                 * cannot have been preempted by the hypervisor, even if it
                 * has called H_CONFER, which will set the yield bit.
                 */
@@ -174,15 +189,17 @@ static inline bool vcpu_is_preempted(int cpu)
                        return false;
 
                /*
-                * If any of the threads of the target CPU's core are not
-                * preempted or ceded, then consider target CPU to be
-                * non-preempted.
+                * The specific target CPU was marked by guest OS as idle, but
+                * then also check all other cpus in the core for PowerVM
+                * because it does core scheduling and one of the vcpu
+                * of the core getting preempted by hypervisor implies
+                * other vcpus can also be considered preempted.
                 */
                first_cpu = cpu_first_thread_sibling(cpu);
                for (i = first_cpu; i < first_cpu + threads_per_core; i++) {
                        if (i == cpu)
                                continue;
-                       if (!(yield_count_of(i) & 1))
+                       if (vcpu_is_dispatched(i))
                                return false;
                        if (!is_vcpu_idle(i))
                                return true;