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....@linux.intel.com> Cc: "K. Y. Srinivasan" <k...@microsoft.com> Cc: Haiyang Zhang <haiya...@microsoft.com> Cc: Stephen Hemminger <sthem...@microsoft.com> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Michael Kelley (EOSG) <michael.h.kel...@microsoft.com> Cc: Juergen Gross <jgr...@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