x86/hyperv: Micro-optimize send_ipi_one()

When sending an IPI to a single CPU there is no need to deal with cpumasks.

With 2 CPU guest on WS2019 a minor (like 3%, 8043 -> 7761 CPU cycles)
improvement with smp_call_function_single() loop benchmark can be seeb. The
optimization, however, is tiny and straitforward. Also, send_ipi_one() is
important for PV spinlock kick.

Switching to the regular APIC IPI send for CPU > 64 case does not make
sense as it is twice as expesive (12650 CPU cycles for __send_ipi_mask_ex()
call, 26000 for orig_apic.send_IPI(cpu, vector)).

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Reviewed-by: Roman Kagan <rkagan@virtuozzo.com>
Link: https://lkml.kernel.org/r/20191027151938.7296-1-vkuznets@redhat.com

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 5c056b8aebefc83468729d0a8bba6e171914c21e..86c8674e92f421a8c355783a5b59ce753e744ee2 100644 (file)
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -194,10 +194,20 @@ do_ex_hypercall:
 
 static bool __send_ipi_one(int cpu, int vector)
 {
-       struct cpumask mask = CPU_MASK_NONE;
+       int vp = hv_cpu_number_to_vp_number(cpu);
 
-       cpumask_set_cpu(cpu, &mask);
-       return __send_ipi_mask(&mask, vector);
+       trace_hyperv_send_ipi_one(cpu, vector);
+
+       if (!hv_hypercall_pg || (vp == VP_INVAL))
+               return false;
+
+       if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))
+               return false;
+
+       if (vp >= 64)
+               return __send_ipi_mask_ex(cpumask_of(cpu), vector);
+
+       return !hv_do_fast_hypercall16(HVCALL_SEND_IPI, vector, BIT_ULL(vp));
 }
 
 static void hv_send_ipi(int cpu, int vector)

diff --git a/arch/x86/include/asm/trace/hyperv.h b/arch/x86/include/asm/trace/hyperv.h
index ace464f09681a3178e2fc8751573eba877009478..4d705cb4d63bed3ede763563a1cbe35b631b4c85 100644 (file)
--- a/arch/x86/include/asm/trace/hyperv.h
+++ b/arch/x86/include/asm/trace/hyperv.h
@@ -71,6 +71,21 @@ TRACE_EVENT(hyperv_send_ipi_mask,
                      __entry->ncpus, __entry->vector)
        );
 
+TRACE_EVENT(hyperv_send_ipi_one,
+           TP_PROTO(int cpu,
+                    int vector),
+           TP_ARGS(cpu, vector),
+           TP_STRUCT__entry(
+                   __field(int, cpu)
+                   __field(int, vector)
+                   ),
+           TP_fast_assign(__entry->cpu = cpu;
+                          __entry->vector = vector;
+                   ),
+           TP_printk("cpu %d vector %x",
+                     __entry->cpu, __entry->vector)
+       );
+
 #endif /* CONFIG_HYPERV */
 
 #undef TRACE_INCLUDE_PATH