Waiman Long
2017-Feb-10 15:43 UTC
[PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
It was found when running fio sequential write test with a XFS ramdisk
on a VM running on a 2-socket x86-64 system, the %CPU times as reported
by perf were as follows:
69.75% 0.59% fio [k] down_write
69.15% 0.01% fio [k] call_rwsem_down_write_failed
67.12% 1.12% fio [k] rwsem_down_write_failed
63.48% 52.77% fio [k] osq_lock
9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt
3.93% 3.93% fio [k] __kvm_vcpu_is_preempted
Making vcpu_is_preempted() a callee-save function has a relatively
high cost on x86-64 primarily due to at least one more cacheline of
data access from the saving and restoring of registers (8 of them)
to and from stack as well as one more level of function call. 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 on both bare-metal & KVM guest on a 2-socekt
16-core 32-thread system with 16 parallel jobs (8 on each socket), the
aggregrate bandwidth of the fio test on an XFS ramdisk were as follows:
Bare Metal KVM Guest
I/O Type w/o patch with patch w/o patch with patch
-------- --------- ---------- --------- ----------
random read 8650.5 MB/s 8560.9 MB/s 7602.9 MB/s 8196.1 MB/s
seq read 9104.8 MB/s 9397.2 MB/s 8293.7 MB/s 8566.9 MB/s
random write 1623.8 MB/s 1626.7 MB/s 1590.6 MB/s 1700.7 MB/s
seq write 1626.4 MB/s 1624.9 MB/s 1604.8 MB/s 1726.3 MB/s
The perf data (on KVM guest) now became:
70.78% 0.58% fio [k] down_write
70.20% 0.01% fio [k] call_rwsem_down_write_failed
69.70% 1.17% fio [k] rwsem_down_write_failed
59.91% 55.42% fio [k] osq_lock
10.14% 10.14% fio [k] __kvm_vcpu_is_preempted
On bare metal, the patch doesn't introduce any performance
regression. On KVM guest, it produces noticeable performance
improvement (up to 7%).
Signed-off-by: Waiman Long <longman at redhat.com>
---
v1->v2:
- Rerun the fio test on a different system on both bare-metal and a
KVM guest. Both sockets were utilized in this test.
- The commit log was updated with new performance numbers, but the
patch wasn't changed.
- Drop patch 2.
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
Peter Zijlstra
2017-Feb-10 16:19 UTC
[PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On Fri, Feb 10, 2017 at 10:43:09AM -0500, Waiman Long wrote:> It was found when running fio sequential write test with a XFS ramdisk > on a VM running on a 2-socket x86-64 system, the %CPU times as reported > by perf were as follows: > > 69.75% 0.59% fio [k] down_write > 69.15% 0.01% fio [k] call_rwsem_down_write_failed > 67.12% 1.12% fio [k] rwsem_down_write_failed > 63.48% 52.77% fio [k] osq_lock > 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt > 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted >Thinking about this again, wouldn't something like the below also work? diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c index 099fcba4981d..6aa33702c15c 100644 --- a/arch/x86/kernel/kvm.c +++ b/arch/x86/kernel/kvm.c @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val) local_irq_restore(flags); } +#ifdef CONFIG_X86_32 __visible bool __kvm_vcpu_is_preempted(int cpu) { struct kvm_steal_time *src = &per_cpu(steal_time, cpu); @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) } PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); +#else + +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int); + +asm( +".pushsection .text;" +".global __raw_callee_save___kvm_vcpu_is_preempted;" +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;" +"__raw_callee_save___kvm_vcpu_is_preempted:" +FRAME_BEGIN +"push %rdi;" +"push %rdx;" +"movslq %edi, %rdi;" +"movq $steal_time+16, %rax;" +"movq __per_cpu_offset(,%rdi,8), %rdx;" +"cmpb $0, (%rdx,%rax);" +"setne %al;" +"pop %rdx;" +"pop %rdi;" +FRAME_END +"ret;" +".popsection"); + +#endif + /* * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. */
Paolo Bonzini
2017-Feb-10 16:22 UTC
[PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 10/02/2017 16:43, Waiman Long wrote:> It was found when running fio sequential write test with a XFS ramdisk > on a VM running on a 2-socket x86-64 system, the %CPU times as reported > by perf were as follows: > > 69.75% 0.59% fio [k] down_write > 69.15% 0.01% fio [k] call_rwsem_down_write_failed > 67.12% 1.12% fio [k] rwsem_down_write_failed > 63.48% 52.77% fio [k] osq_lock > 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt > 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted > > Making vcpu_is_preempted() a callee-save function has a relatively > high cost on x86-64 primarily due to at least one more cacheline of > data access from the saving and restoring of registers (8 of them) > to and from stack as well as one more level of function call. 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 on both bare-metal & KVM guest on a 2-socekt > 16-core 32-thread system with 16 parallel jobs (8 on each socket), the > aggregrate bandwidth of the fio test on an XFS ramdisk were as follows: > > Bare Metal KVM Guest > I/O Type w/o patch with patch w/o patch with patch > -------- --------- ---------- --------- ---------- > random read 8650.5 MB/s 8560.9 MB/s 7602.9 MB/s 8196.1 MB/s > seq read 9104.8 MB/s 9397.2 MB/s 8293.7 MB/s 8566.9 MB/s > random write 1623.8 MB/s 1626.7 MB/s 1590.6 MB/s 1700.7 MB/s > seq write 1626.4 MB/s 1624.9 MB/s 1604.8 MB/s 1726.3 MB/s > > The perf data (on KVM guest) now became: > > 70.78% 0.58% fio [k] down_write > 70.20% 0.01% fio [k] call_rwsem_down_write_failed > 69.70% 1.17% fio [k] rwsem_down_write_failed > 59.91% 55.42% fio [k] osq_lock > 10.14% 10.14% fio [k] __kvm_vcpu_is_preempted > > On bare metal, the patch doesn't introduce any performance > regression. On KVM guest, it produces noticeable performance > improvement (up to 7%). > > Signed-off-by: Waiman Long <longman at redhat.com> > --- > v1->v2: > - Rerun the fio test on a different system on both bare-metal and a > KVM guest. Both sockets were utilized in this test. > - The commit log was updated with new performance numbers, but the > patch wasn't changed. > - Drop patch 2. > > 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) >Acked-by: Paolo Bonzini <pbonzini at redhat.com> Thank you very much! Paolo
Waiman Long
2017-Feb-10 16:35 UTC
[PATCH v2] x86/paravirt: Don't make vcpu_is_preempted() a callee-save function
On 02/10/2017 11:19 AM, Peter Zijlstra wrote:> On Fri, Feb 10, 2017 at 10:43:09AM -0500, Waiman Long wrote: >> It was found when running fio sequential write test with a XFS ramdisk >> on a VM running on a 2-socket x86-64 system, the %CPU times as reported >> by perf were as follows: >> >> 69.75% 0.59% fio [k] down_write >> 69.15% 0.01% fio [k] call_rwsem_down_write_failed >> 67.12% 1.12% fio [k] rwsem_down_write_failed >> 63.48% 52.77% fio [k] osq_lock >> 9.46% 7.88% fio [k] __raw_callee_save___kvm_vcpu_is_preempt >> 3.93% 3.93% fio [k] __kvm_vcpu_is_preempted >> > Thinking about this again, wouldn't something like the below also work? > > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index 099fcba4981d..6aa33702c15c 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -589,6 +589,7 @@ static void kvm_wait(u8 *ptr, u8 val) > local_irq_restore(flags); > } > > +#ifdef CONFIG_X86_32 > __visible bool __kvm_vcpu_is_preempted(int cpu) > { > struct kvm_steal_time *src = &per_cpu(steal_time, cpu); > @@ -597,6 +598,31 @@ __visible bool __kvm_vcpu_is_preempted(int cpu) > } > PV_CALLEE_SAVE_REGS_THUNK(__kvm_vcpu_is_preempted); > > +#else > + > +extern bool __raw_callee_save___kvm_vcpu_is_preempted(int); > + > +asm( > +".pushsection .text;" > +".global __raw_callee_save___kvm_vcpu_is_preempted;" > +".type __raw_callee_save___kvm_vcpu_is_preempted, @function;" > +"__raw_callee_save___kvm_vcpu_is_preempted:" > +FRAME_BEGIN > +"push %rdi;" > +"push %rdx;" > +"movslq %edi, %rdi;" > +"movq $steal_time+16, %rax;" > +"movq __per_cpu_offset(,%rdi,8), %rdx;" > +"cmpb $0, (%rdx,%rax);" > +"setne %al;" > +"pop %rdx;" > +"pop %rdi;" > +FRAME_END > +"ret;" > +".popsection"); > + > +#endif > + > /* > * Setup pv_lock_ops to exploit KVM_FEATURE_PV_UNHALT if present. > */That should work for now. I have done something similar for __pv_queued_spin_unlock. However, this has the problem of creating a dependency on the exact layout of the steal_time structure. Maybe the constant 16 can be passed in as a parameter offsetof(struct kvm_steal_time, preempted) to the asm call. Cheers, Longman
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