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x86/paravirt: Optimize native pv_lock_ops.vcpu_is_preempted()

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Avoid the pointless function call to pv_lock_ops.vcpu_is_preempted()
when a paravirt spinlock enabled kernel is ran on native hardware.

Do this by patching out the CALL instruction with "XOR %RAX,%RAX"
which has the same effect (0 return value).

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: David.Laight@ACULAB.COM
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: benh@kernel.crashing.org
Cc: boqun.feng@gmail.com
Cc: borntraeger@de.ibm.com
Cc: bsingharora@gmail.com
Cc: dave@stgolabs.net
Cc: jgross@suse.com
Cc: kernellwp@gmail.com
Cc: konrad.wilk@oracle.com
Cc: mpe@ellerman.id.au
Cc: paulmck@linux.vnet.ibm.com
Cc: paulus@samba.org
Cc: pbonzini@redhat.com
Cc: rkrcmar@redhat.com
Cc: will.deacon@arm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra
2016-11-15 16:47:06 +01:00
committed by Ingo Molnar
parent 05ffc95139
commit 3cded41794
9 changed files with 54 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files

25
arch/x86/kernel/kvm.c
View File

@@ -415,15 +415,6 @@ void kvm_disable_steal_time(void)
wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
}
static bool kvm_vcpu_is_preempted(int cpu)
{
struct kvm_steal_time *src;
src = &per_cpu(steal_time, cpu);
return !!src->preempted;
}
#ifdef CONFIG_SMP
static void __init kvm_smp_prepare_boot_cpu(void)
{
@@ -480,9 +471,6 @@ void __init kvm_guest_init(void)
if (kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
has_steal_clock = 1;
pv_time_ops.steal_clock = kvm_steal_clock;
#ifdef CONFIG_PARAVIRT_SPINLOCKS
pv_lock_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
#endif
}
if (kvm_para_has_feature(KVM_FEATURE_PV_EOI))
@@ -604,6 +592,14 @@ out:
local_irq_restore(flags);
}
__visible bool __kvm_vcpu_is_preempted(int cpu)
{
struct kvm_steal_time *src = &per_cpu(steal_time, 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.
*/
@@ -620,6 +616,11 @@ void __init kvm_spinlock_init(void)
pv_lock_ops.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
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);
}
}
static __init int kvm_spinlock_init_jump(void)