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Subject[PATCH v1 2/2] x86/hyperv: make HvNotifyLongSpinWait hypercall
Date
The HvNotifyLongSpinWait hypercall (HVCALL_NOTIFY_LONG_SPIN_WAIT)
is used by a guest OS to notify the hypervisor that the calling
virtual processor is attempting to acquire a resource that is
potentially held by another virtual processor within the same
Virtual Machine. This scheduling hint improves the scalability of
VMs with more than one virtual processor on Hyper-V.

Per MSFT TLFS, the retry number (SpinWaitInfo) is sent to hypervisor
only when the retry number exceeds the recommended number. If
recommended number is 0xFFFFFFFF, never retry.

Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Michael Kelley (EOSG) <Michael.H.Kelley@microsoft.com>
Cc: Juergen Gross <jgross@suse.com>
---
arch/x86/hyperv/hv_spinlock.c | 18 ++++++++++++++++++
arch/x86/include/asm/mshyperv.h | 1 +
kernel/locking/qspinlock_paravirt.h | 10 ++++++++++
3 files changed, 29 insertions(+)

diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
index a861b04..723dccb 100644
--- a/arch/x86/hyperv/hv_spinlock.c
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -18,6 +18,24 @@

static bool __initdata hv_pvspin = true;

+bool hv_notify_long_spin_wait(int retry_num)
+{
+ /*
+ * Per MSFT TLFS, the SpinWaitInfo is sent to hypervisor only when
+ * the retry number exceeds the recommended number.
+ *
+ * If recommended number is 0xFFFFFFFF, never retry.
+ */
+ if (ms_hyperv.num_spin_retry == HYPERV_SPINLOCK_RETRY_NEVER)
+ return false;
+
+ if ((0 == retry_num % ms_hyperv.num_spin_retry) && retry_num)
+ hv_do_fast_hypercall8(HVCALL_NOTIFY_LONG_SPIN_WAIT,
+ retry_num);
+
+ return true;
+}
+
static void hv_qlock_kick(int cpu)
{
apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR);
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index f909365..bd87868 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -356,6 +356,7 @@ static inline int cpumask_to_vpset(struct hv_vpset *vpset,
void hv_apic_init(void);
void __init hv_init_spinlocks(void);
bool hv_vcpu_is_preempted(int vcpu);
+bool hv_notify_long_spin_wait(int retry_num);
#else
static inline void hv_apic_init(void) {}
#endif
diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
index 0130e48..9e88c7e 100644
--- a/kernel/locking/qspinlock_paravirt.h
+++ b/kernel/locking/qspinlock_paravirt.h
@@ -7,6 +7,8 @@
#include <linux/bootmem.h>
#include <linux/debug_locks.h>

+#include <asm/mshyperv.h>
+
/*
* Implement paravirt qspinlocks; the general idea is to halt the vcpus instead
* of spinning them.
@@ -305,6 +307,10 @@ static void pv_wait_node(struct mcs_spinlock *node, struct mcs_spinlock *prev)
wait_early = true;
break;
}
+#if defined(CONFIG_X86_64) && defined(CONFIG_PARAVIRT_SPINLOCKS) && IS_ENABLED(CONFIG_HYPERV)
+ if (!hv_notify_long_spin_wait(SPIN_THRESHOLD - loop))
+ break;
+#endif
cpu_relax();
}

@@ -433,6 +439,10 @@ static void pv_kick_node(struct qspinlock *lock, struct mcs_spinlock *node)
for (loop = SPIN_THRESHOLD; loop; loop--) {
if (trylock_clear_pending(lock))
goto gotlock;
+#if defined(CONFIG_X86_64) && defined(CONFIG_PARAVIRT_SPINLOCKS) && IS_ENABLED(CONFIG_HYPERV)
+ if (!hv_notify_long_spin_wait(SPIN_THRESHOLD - loop))
+ break;
+#endif
cpu_relax();
}
clear_pending(lock);
--
1.9.1
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