[PATCH 1/2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
From: Waiman Long <longman@redhat.com>
Date: 2017-02-08 18:01:37
Also in:
kvm, linux-arch, lkml
Subsystem:
kvm paravirt (kvm/paravirt), paravirt_ops interface, the rest, x86 architecture (32-bit and 64-bit), xen hypervisor x86 · Maintainers:
Paolo Bonzini, Juergen Gross, Linus Torvalds, Thomas Gleixner, Ingo Molnar, Borislav Petkov, Dave Hansen
It was found when running fio sequential write test with a XFS ramdisk on a 2-socket x86-64 system, the %CPU times as reported by perf were as follows: 71.27% 0.28% fio [k] down_write 70.99% 0.01% fio [k] call_rwsem_down_write_failed 69.43% 1.18% fio [k] rwsem_down_write_failed 65.51% 54.57% fio [k] osq_lock 9.72% 7.99% fio [k] __raw_callee_save___kvm_vcpu_is_preempted 4.16% 4.16% fio [k] __kvm_vcpu_is_preempted So making vcpu_is_preempted() a callee-save function has a pretty high cost associated with it. As vcpu_is_preempted() is called within the spinlock, mutex and rwsem slowpaths, there isn't much to gain by making it callee-save. So it is now changed to a normal function call instead. With this patch applied, the aggregrate bandwidth of the fio sequential write test increased slightly from 2563.3MB/s to 2588.1MB/s (about 1%). Signed-off-by: Waiman Long <longman@redhat.com> --- arch/x86/include/asm/paravirt.h | 2 +- arch/x86/include/asm/paravirt_types.h | 2 +- arch/x86/kernel/kvm.c | 7 ++----- arch/x86/kernel/paravirt-spinlocks.c | 6 ++---- arch/x86/xen/spinlock.c | 4 +--- 5 files changed, 7 insertions(+), 14 deletions(-)
diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 864f57b..2515885 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h@@ -676,7 +676,7 @@ static __always_inline void pv_kick(int cpu) static __always_inline bool pv_vcpu_is_preempted(int cpu) { - return PVOP_CALLEE1(bool, pv_lock_ops.vcpu_is_preempted, cpu); + return PVOP_CALL1(bool, pv_lock_ops.vcpu_is_preempted, cpu); } #endif /* SMP && PARAVIRT_SPINLOCKS */
diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index bb2de45..88dc852 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h@@ -309,7 +309,7 @@ struct pv_lock_ops { void (*wait)(u8 *ptr, u8 val); void (*kick)(int cpu); - struct paravirt_callee_save vcpu_is_preempted; + bool (*vcpu_is_preempted)(int cpu); }; /* This contains all the paravirt structures: we get a convenient
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index 099fcba..eb3753d 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c@@ -595,7 +595,6 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) return !!src->preempted; } -PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present.
@@ -614,10 +613,8 @@ void __init kvm_spinlock_init(void) pv_lock_ops.wait = kvm_wait; pv_lock_ops.kick = kvm_kick_cpu; - if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) { - pv_lock_ops.vcpu_is_preempted = - PV_CALLEE_SAVE(__kvm_vcpu_is_preempted); - } + if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) + pv_lock_ops.vcpu_is_preempted = __kvm_vcpu_is_preempted; } #endif /* CONFIG_PARAVIRT_SPINLOCKS */
diff --git a/arch/x86/kernel/paravirt-spinlocks.c b/arch/x86/kernel/paravirt-spinlocks.c
index 6259327..da050bc 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c@@ -24,12 +24,10 @@ __visible bool __native_vcpu_is_preempted(int cpu) { return false; } -PV_CALLEE_SAVE_REGS_THUNK(__native_vcpu_is_preempted); bool pv_is_native_vcpu_is_preempted(void) { - return pv_lock_ops.vcpu_is_preempted.func == - __raw_callee_save___native_vcpu_is_preempted; + return pv_lock_ops.vcpu_is_preempted == __native_vcpu_is_preempted; } struct pv_lock_ops pv_lock_ops = {
@@ -38,7 +36,7 @@ struct pv_lock_ops pv_lock_ops = { .queued_spin_unlock = PV_CALLEE_SAVE(__native_queued_spin_unlock), .wait = paravirt_nop, .kick = paravirt_nop, - .vcpu_is_preempted = PV_CALLEE_SAVE(__native_vcpu_is_preempted), + .vcpu_is_preempted = __native_vcpu_is_preempted, #endif /* SMP */ }; EXPORT_SYMBOL(pv_lock_ops);
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 25a7c43..c85bb8f 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c@@ -114,8 +114,6 @@ void xen_uninit_lock_cpu(int cpu) per_cpu(irq_name, cpu) = NULL; } -PV_CALLEE_SAVE_REGS_THUNK(xen_vcpu_stolen); - /* * Our init of PV spinlocks is split in two init functions due to us * using paravirt patching and jump labels patching and having to do
@@ -138,7 +136,7 @@ void __init xen_init_spinlocks(void) pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock); pv_lock_ops.wait = xen_qlock_wait; pv_lock_ops.kick = xen_qlock_kick; - pv_lock_ops.vcpu_is_preempted = PV_CALLEE_SAVE(xen_vcpu_stolen); + pv_lock_ops.vcpu_is_preempted = xen_vcpu_stolen; } static __init int xen_parse_nopvspin(char *arg)
--
1.8.3.1