[Xen-devel] [PATCH RFC V11 7/18] x86/pvticketlock: Use callee-save for lock_spinning

[Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>]

x86/pvticketlock: Use callee-save for lock_spinning

From: Jeremy Fitzhardinge <jeremy@xxxxxxxx>

Although the lock_spinning calls in the spinlock code are on the
uncommon path, their presence can cause the compiler to generate many
more register save/restores in the function pre/postamble, which is in
the fast path.  To avoid this, convert it to using the pvops callee-save
calling convention, which defers all the save/restores until the actual
function is called, keeping the fastpath clean.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xxxxxxxx>
Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Tested-by: Attilio Rao <attilio.rao@xxxxxxxxxx>
Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx>
---
 arch/x86/include/asm/paravirt.h       |    2 +-
 arch/x86/include/asm/paravirt_types.h |    2 +-
 arch/x86/kernel/paravirt-spinlocks.c  |    2 +-
 arch/x86/xen/spinlock.c               |    3 ++-
 4 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/paravirt.h b/arch/x86/include/asm/paravirt.h
index 040e72d..7131e12c 100644
--- a/arch/x86/include/asm/paravirt.h
+++ b/arch/x86/include/asm/paravirt.h
@@ -715,7 +715,7 @@ static inline void __set_fixmap(unsigned /* enum 
fixed_addresses */ idx,
 static __always_inline void __ticket_lock_spinning(struct arch_spinlock *lock,
                                                        __ticket_t ticket)
 {
-       PVOP_VCALL2(pv_lock_ops.lock_spinning, lock, ticket);
+       PVOP_VCALLEE2(pv_lock_ops.lock_spinning, lock, ticket);
 }
 
 static __always_inline void ____ticket_unlock_kick(struct arch_spinlock *lock,
diff --git a/arch/x86/include/asm/paravirt_types.h 
b/arch/x86/include/asm/paravirt_types.h
index d5deb6d..350d017 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -330,7 +330,7 @@ struct arch_spinlock;
 #include <asm/spinlock_types.h>
 
 struct pv_lock_ops {
-       void (*lock_spinning)(struct arch_spinlock *lock, __ticket_t ticket);
+       struct paravirt_callee_save lock_spinning;
        void (*unlock_kick)(struct arch_spinlock *lock, __ticket_t ticket);
 };
 
diff --git a/arch/x86/kernel/paravirt-spinlocks.c 
b/arch/x86/kernel/paravirt-spinlocks.c
index c2e010e..4251c1d 100644
--- a/arch/x86/kernel/paravirt-spinlocks.c
+++ b/arch/x86/kernel/paravirt-spinlocks.c
@@ -9,7 +9,7 @@
 
 struct pv_lock_ops pv_lock_ops = {
 #ifdef CONFIG_SMP
-       .lock_spinning = paravirt_nop,
+       .lock_spinning = __PV_IS_CALLEE_SAVE(paravirt_nop),
        .unlock_kick = paravirt_nop,
 #endif
 };
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index ec9183b..b41872b 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -173,6 +173,7 @@ out:
        local_irq_restore(flags);
        spin_time_accum_blocked(start);
 }
+PV_CALLEE_SAVE_REGS_THUNK(xen_lock_spinning);
 
 static void xen_unlock_kick(struct arch_spinlock *lock, __ticket_t next)
 {
@@ -260,7 +261,7 @@ void __init xen_init_spinlocks(void)
                return;
        }
 
-       pv_lock_ops.lock_spinning = xen_lock_spinning;
+       pv_lock_ops.lock_spinning = PV_CALLEE_SAVE(xen_lock_spinning);
        pv_lock_ops.unlock_kick = xen_unlock_kick;
 }
 


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