search for: virt_spin_lock_key

With virt_spin_lock() being guarded by a static key the bare metal case can be optimized by patching the call away completely. In case a kernel running as a guest it can decide whether to use paravitualized spinlocks, the current fallback to the unfair test-and-set scheme, or to mimic the bare metal behavior. V2: - use static key instead of making virt_spin_lock() a pvops function Juergen Gross

With virt_spin_lock() being guarded by a static key the bare metal case can be optimized by patching the call away completely. In case a kernel running as a guest it can decide whether to use paravitualized spinlocks, the current fallback to the unfair test-and-set scheme, or to mimic the bare metal behavior. V2: - use static key instead of making virt_spin_lock() a pvops function Juergen Gross

...why you are reporting this for 4.14-rc6. Ah sorry, I simply checked recent bisects for that warning. Then I'll need to carry out some new bisect on 4.14-rc6. >There is a patch by Dou Liyang pending since 28th October addressing >that issue: > >[PATCH tip v2] x86/paravirt: Make the virt_spin_lock_key setup after >jump_label_init() Excellent! Thanks, Fengguang

...why you are reporting this for 4.14-rc6. Ah sorry, I simply checked recent bisects for that warning. Then I'll need to carry out some new bisect on 4.14-rc6. >There is a patch by Dou Liyang pending since 28th October addressing >that issue: > >[PATCH tip v2] x86/paravirt: Make the virt_spin_lock_key setup after >jump_label_init() Excellent! Thanks, Fengguang

.../jump_label.c:#static_key_disable_cpuslocked: 7 This patch is in the tip tree only, it will be merged in 4.15. So I don't understand why you are reporting this for 4.14-rc6. There is a patch by Dou Liyang pending since 28th October addressing that issue: [PATCH tip v2] x86/paravirt: Make the virt_spin_lock_key setup after jump_label_init() Juergen > > The call trace is > > [??? 0.000000] Booting paravirtualized kernel on bare hardware > [??? 0.000000] clocksource: refined-jiffies: mask: 0xffffffff > max_cycles: 0xffffffff, max_idle_ns: 1910969940391419 ns > [??? 0.000000] setup_...

...gt; > #include <asm/cpufeature.h> > #include <asm-generic/qspinlock_types.h> > #include <asm/paravirt.h> > @@ -46,9 +47,15 @@ static inline void queued_spin_unlock(struct qspinlock *lock) > #endif > > #ifdef CONFIG_PARAVIRT > +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +void native_pv_lock_init(void) __init; > + > #define virt_spin_lock virt_spin_lock > static inline bool virt_spin_lock(struct qspinlock *lock) > { > + if (!static_branch_likely(&virt_spin_lock_key)) > + return false; > if (!static_cpu_has(X86_FEATURE_HY...

...gt; > #include <asm/cpufeature.h> > #include <asm-generic/qspinlock_types.h> > #include <asm/paravirt.h> > @@ -46,9 +47,15 @@ static inline void queued_spin_unlock(struct qspinlock *lock) > #endif > > #ifdef CONFIG_PARAVIRT > +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +void native_pv_lock_init(void) __init; > + > #define virt_spin_lock virt_spin_lock > static inline bool virt_spin_lock(struct qspinlock *lock) > { > + if (!static_branch_likely(&virt_spin_lock_key)) > + return false; > if (!static_cpu_has(X86_FEATURE_HY...

...CK_H +#include <linux/jump_label.h> #include <asm/cpufeature.h> #include <asm-generic/qspinlock_types.h> #include <asm/paravirt.h> @@ -46,9 +47,15 @@ static inline void queued_spin_unlock(struct qspinlock *lock) #endif #ifdef CONFIG_PARAVIRT +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); + +void native_pv_lock_init(void) __init; + #define virt_spin_lock virt_spin_lock static inline bool virt_spin_lock(struct qspinlock *lock) { + if (!static_branch_likely(&virt_spin_lock_key)) + return false; if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) return false; @@ -65,6 +72,10...

With virt_spin_lock() being guarded by a static key the bare metal case can be optimized by patching the call away completely. In case a kernel running as a guest it can decide whether to use paravitualized spinlocks, the current fallback to the unfair test-and-set scheme, or to mimic the bare metal behavior. V3: - remove test for hypervisor environment from virt_spin_lock(9 as suggested by

With virt_spin_lock() being guarded by a static key the bare metal case can be optimized by patching the call away completely. In case a kernel running as a guest it can decide whether to use paravitualized spinlocks, the current fallback to the unfair test-and-set scheme, or to mimic the bare metal behavior. V3: - remove test for hypervisor environment from virt_spin_lock(9 as suggested by

...pe = locktype_paravirt; + else if (!strcmp(s, "unfair")) + pv_spinlock_type = locktype_unfair; + else + return -EINVAL; + + pr_info("PV lock type = %s (%d)\n", s, pv_spinlock_type); + return 0; +} + +early_param("pvlock_type", pvlock_setup); + DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); void __init native_pv_lock_init(void) { - if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) + if (pv_spinlock_type == locktype_unfair) + return; + + if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || + (pv_spinlock_type != locktype_auto)) static_branch_disable(&virt_spin_lock_key); } @@...

...pe = locktype_paravirt; + else if (!strcmp(s, "unfair")) + pv_spinlock_type = locktype_unfair; + else + return -EINVAL; + + pr_info("PV lock type = %s (%d)\n", s, pv_spinlock_type); + return 0; +} + +early_param("pvlock_type", pvlock_setup); + DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); void __init native_pv_lock_init(void) { - if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) + if (pv_spinlock_type == locktype_unfair) + return; + + if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || + (pv_spinlock_type != locktype_auto)) static_branch_disable(&virt_spin_lock_key); } @@...

v1->v2: - Make pv_spinlock_type a bit mask for easier checking. - Add patch 2 to deprecate xen_nopvspin v1 - https://lkml.org/lkml/2017/11/1/381 Patch 1 adds a new pvlock_type parameter for the administrators to specify the type of lock to be used in a para-virtualized kernel. Patch 2 deprecates Xen's xen_nopvspin parameter as it is no longer needed. Waiman Long (2): x86/paravirt:

v1->v2: - Make pv_spinlock_type a bit mask for easier checking. - Add patch 2 to deprecate xen_nopvspin v1 - https://lkml.org/lkml/2017/11/1/381 Patch 1 adds a new pvlock_type parameter for the administrators to specify the type of lock to be used in a para-virtualized kernel. Patch 2 deprecates Xen's xen_nopvspin parameter as it is no longer needed. Waiman Long (2): x86/paravirt:

...parameter "xen_nopvspin" specified a Xen guest should not make use of paravirt spinlocks, but behave as if running on bare metal. This is not true, however, as the qspinlock code will fall back to a test-and-set scheme when it is detecting a hypervisor. In order to avoid this disable the virt_spin_lock_key. Signed-off-by: Juergen Gross <jgross at suse.com> --- arch/x86/xen/spinlock.c | 2 ++ 1 file changed, 2 insertions(+) diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c index 25a7c4302ce7..e8ab80ad7a6f 100644 --- a/arch/x86/xen/spinlock.c +++ b/arch/x86/xen/spinlock.c @@ -10,6...

On 09/06/2017 12:04 PM, Peter Zijlstra wrote: > On Wed, Sep 06, 2017 at 11:49:49AM -0400, Waiman Long wrote: >>> #define virt_spin_lock virt_spin_lock >>> static inline bool virt_spin_lock(struct qspinlock *lock) >>> { >>> + if (!static_branch_likely(&virt_spin_lock_key)) >>> + return false; >>> if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) >>> return false; >>> > Now native has two NOPs instead of one. Can't we merge these two static > branches? I guess we can remove the static_cpu_has() call. Just that any s...

On 09/06/2017 12:04 PM, Peter Zijlstra wrote: > On Wed, Sep 06, 2017 at 11:49:49AM -0400, Waiman Long wrote: >>> #define virt_spin_lock virt_spin_lock >>> static inline bool virt_spin_lock(struct qspinlock *lock) >>> { >>> + if (!static_branch_likely(&virt_spin_lock_key)) >>> + return false; >>> if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) >>> return false; >>> > Now native has two NOPs instead of one. Can't we merge these two static > branches? I guess we can remove the static_cpu_has() call. Just that any s...

...air")) > + pv_spinlock_type = locktype_unfair; > + else > + return -EINVAL; > + > + pr_info("PV lock type = %s (%d)\n", s, pv_spinlock_type); > + return 0; > +} > + > +early_param("pvlock_type", pvlock_setup); > + > DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); > > void __init native_pv_lock_init(void) > { > - if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) > + if (pv_spinlock_type == locktype_unfair) > + return; > + > + if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || > + (pv_spinlock_type != locktype_auto)) > static...

...Xen's xen_nopvspin in term of disabling unfair lock. > Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others > think? I don't think we need xen_nopvspin, but I don't want to remove that without agreement from the community. >> DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); >> >> void __init native_pv_lock_init(void) >> { >> - if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) >> + if (pv_spinlock_type == locktype_unfair) >> + return; >> + >> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || >> + (pv_spinlock_ty...

...Xen's xen_nopvspin in term of disabling unfair lock. > Hmm, I'm not sure we need pvlock_type _and_ xen_nopvspin. What do others > think? I don't think we need xen_nopvspin, but I don't want to remove that without agreement from the community. >> DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); >> >> void __init native_pv_lock_init(void) >> { >> - if (!static_cpu_has(X86_FEATURE_HYPERVISOR)) >> + if (pv_spinlock_type == locktype_unfair) >> + return; >> + >> + if (!static_cpu_has(X86_FEATURE_HYPERVISOR) || >> + (pv_spinlock_ty...