Commit b264f57f authored by Vitaly Kuznetsov's avatar Vitaly Kuznetsov Committed by Thomas Gleixner
Browse files

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: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarMichael Kelley <mikelley@microsoft.com>
Reviewed-by: default avatarRoman Kagan <rkagan@virtuozzo.com>
Link: https://lkml.kernel.org/r/20191027151938.7296-1-vkuznets@redhat.com
parent 83527ef7

arch/x86/hyperv/hv_apic.c

+13 −3
Original line number Diff line number Diff line
@@ -194,10 +194,20 @@ 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;

	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)

arch/x86/include/asm/trace/hyperv.h

+15 −0
Original line number Diff line number Diff line
@@ -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