[PATCH v2] x86/hyper-v: micro-optimize send_ipi_one case
From: Vitaly Kuznetsov <vkuznets@redhat.com>
Date: 2019-10-25 13:16:00
Also in:
lkml
Subsystem:
hyper-v/azure core and drivers, the rest, x86 architecture (32-bit and 64-bit) · Maintainers:
"K. Y. Srinivasan", Haiyang Zhang, Wei Liu, Dexuan Cui, Long Li, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
When sending an IPI to a single CPU there is no need to deal with cpumasks. With 2 CPU guest on WS2019 I'm seeing a minor (like 3%, 8043 -> 7761 CPU cycles) improvement with smp_call_function_single() loop benchmark. The optimization, however, is tiny and straitforward. Also, send_ipi_one() is important for PV spinlock kick. I was also wondering if it would make sense to switch to using regular APIC IPI send for CPU > 64 case but no, 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> --- Changes since v1: - Style changes [Roman, Joe] --- arch/x86/hyperv/hv_apic.c | 13 ++++++++++--- arch/x86/include/asm/trace/hyperv.h | 15 +++++++++++++++ 2 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index e01078e93dd3..fd17c6341737 100644
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c@@ -194,10 +194,17 @@ static bool __send_ipi_mask(const struct cpumask *mask, int vector) static bool __send_ipi_one(int cpu, int vector) { - struct cpumask mask = CPU_MASK_NONE; + trace_hyperv_send_ipi_one(cpu, vector); - cpumask_set_cpu(cpu, &mask); - return __send_ipi_mask(&mask, vector); + if (!hv_hypercall_pg || (vector < HV_IPI_LOW_VECTOR) || + (vector > HV_IPI_HIGH_VECTOR)) + return false; + + if (cpu >= 64) + return __send_ipi_mask_ex(cpumask_of(cpu), vector); + + return !hv_do_fast_hypercall16(HVCALL_SEND_IPI, vector, + BIT_ULL(hv_cpu_number_to_vp_number(cpu))); } 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 ace464f09681..4d705cb4d63b 100644
--- 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
--
2.20.1