x86/hyper-v: Use cheaper HVCALL_SEND_IPI hypercall when possible

When there is no need to send an IPI to a CPU with VP number > 64
we can do the job with fast HVCALL_SEND_IPI hypercall.

Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Cc: devel@linuxdriverproject.org
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Tianyu Lan <Tianyu.Lan@microsoft.com>
Cc: "Michael Kelley (EOSG)" <Michael.H.Kelley@microsoft.com>
Link: https://lkml.kernel.org/r/20180622170625.30688-4-vkuznets@redhat.com

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 90055f89223b1c4e70dd91a913f42f256f8b3ade..ee962784d25b7ef84a353ae0fc16e07182fdb4c1 100644 (file)
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -99,6 +99,9 @@ static bool __send_ipi_mask_ex(const struct cpumask *mask, int vector)
        int nr_bank = 0;
        int ret = 1;
 
+       if (!(ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED))
+               return false;
+
        local_irq_save(flags);
        arg = (struct ipi_arg_ex **)this_cpu_ptr(hyperv_pcpu_input_arg);
 
@@ -140,8 +143,18 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector)
        if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))
                return false;
 
-       if ((ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED))
-               return __send_ipi_mask_ex(mask, vector);
+       /*
+        * From the supplied CPU set we need to figure out if we can get away
+        * with cheaper HVCALL_SEND_IPI hypercall. This is possible when the
+        * highest VP number in the set is < 64. As VP numbers are usually in
+        * ascending order and match Linux CPU ids, here is an optimization:
+        * we check the VP number for the highest bit in the supplied set first
+        * so we can quickly find out if using HVCALL_SEND_IPI_EX hypercall is
+        * a must. We will also check all VP numbers when walking the supplied
+        * CPU set to remain correct in all cases.
+        */
+       if (hv_cpu_number_to_vp_number(cpumask_last(mask)) >= 64)
+               goto do_ex_hypercall;
 
        ipi_arg.vector = vector;
        ipi_arg.cpu_mask = 0;
@@ -153,16 +166,17 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector)
                 * only target upto 64 CPUs.
                 */
                if (vcpu >= 64)
-                       goto ipi_mask_done;
+                       goto do_ex_hypercall;
 
                __set_bit(vcpu, (unsigned long *)&ipi_arg.cpu_mask);
        }
 
        ret = hv_do_fast_hypercall16(HVCALL_SEND_IPI, ipi_arg.vector,
                                     ipi_arg.cpu_mask);
-
-ipi_mask_done:
        return ((ret == 0) ? true : false);
+
+do_ex_hypercall:
+       return __send_ipi_mask_ex(mask, vector);
 }
 
 static bool __send_ipi_one(int cpu, int vector)
@@ -218,10 +232,7 @@ static void hv_send_ipi_self(int vector)
 void __init hv_apic_init(void)
 {
        if (ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) {
-               if ((ms_hyperv.hints & HV_X64_EX_PROCESSOR_MASKS_RECOMMENDED))
-                       pr_info("Hyper-V: Using ext hypercalls for IPI\n");
-               else
-                       pr_info("Hyper-V: Using IPI hypercalls\n");
+               pr_info("Hyper-V: Using IPI hypercalls\n");
                /*
                 * Set the IPI entry points.
                 */