[PATCH 3/4] x86/hyper-v: use cheaper HVCALL_SEND_IPI hypercall when possible

Vitaly Kuznetsov
2018-06-22T17:06:40Z

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>
---
arch/x86/hyperv/hv_apic.c | 29 ++++++++++++++++++++---------
1 file changed, 20 insertions(+), 9 deletions(-)

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index 90055f89223b..ee962784d25b 100644
--- 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.
*/
--
2.14.4