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* [PATCH] x86/hyper-v: micro-optimize send_ipi_one case
@ 2019-10-24 15:21 Vitaly Kuznetsov
  2019-10-24 16:32 ` Roman Kagan
  2019-10-24 16:47 ` Joe Perches
  0 siblings, 2 replies; 7+ messages in thread
From: Vitaly Kuznetsov @ 2019-10-24 15:21 UTC (permalink / raw)
  To: linux-hyperv
  Cc: linux-kernel, x86, K. Y. Srinivasan, Haiyang Zhang,
	Stephen Hemminger, Sasha Levin, Thomas Gleixner, Ingo Molnar,
	Borislav Petkov, H. Peter Anvin, Roman Kagan, Michael Kelley

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>
---
 arch/x86/hyperv/hv_apic.c           | 22 +++++++++++++++++++---
 arch/x86/include/asm/trace/hyperv.h | 15 +++++++++++++++
 2 files changed, 34 insertions(+), 3 deletions(-)

diff --git a/arch/x86/hyperv/hv_apic.c b/arch/x86/hyperv/hv_apic.c
index e01078e93dd3..847f9d0328fe 100644
--- a/arch/x86/hyperv/hv_apic.c
+++ b/arch/x86/hyperv/hv_apic.c
@@ -194,10 +194,26 @@ 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 ret;
 
-	cpumask_set_cpu(cpu, &mask);
-	return __send_ipi_mask(&mask, vector);
+	trace_hyperv_send_ipi_one(cpu, vector);
+
+	if (unlikely(!hv_hypercall_pg))
+		return false;
+
+	if (unlikely((vector < HV_IPI_LOW_VECTOR) ||
+		     (vector > HV_IPI_HIGH_VECTOR)))
+		return false;
+
+	if (cpu >= 64)
+		goto do_ex_hypercall;
+
+	ret = hv_do_fast_hypercall16(HVCALL_SEND_IPI, vector,
+				     BIT_ULL(hv_cpu_number_to_vp_number(cpu)));
+	return ((ret == 0) ? true : false);
+
+do_ex_hypercall:
+	return __send_ipi_mask_ex(cpumask_of(cpu), vector);
 }
 
 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


^ permalink raw reply related	[flat|nested] 7+ messages in thread

end of thread, other threads:[~2019-10-25 16:24 UTC | newest]

Thread overview: 7+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2019-10-24 15:21 [PATCH] x86/hyper-v: micro-optimize send_ipi_one case Vitaly Kuznetsov
2019-10-24 16:32 ` Roman Kagan
2019-10-24 22:38   ` Thomas Gleixner
2019-10-25  9:41     ` Roman Kagan
2019-10-25 10:44   ` Vitaly Kuznetsov
2019-10-25 16:23     ` Michael Kelley
2019-10-24 16:47 ` Joe Perches

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