Re: [PATCH] kvm: kvmclock: use get_cpu() and put_cpu()

[Paolo Bonzini <pbonzini@redhat.com>]

Il 26/09/2014 08:00, Tiejun Chen ha scritto:
> We can use get_cpu() and put_cpu() to replace
> preempt_disable()/cpu = smp_processor_id() and
> preempt_enable() for slightly better code.
> 
> Signed-off-by: Tiejun Chen <tiejun.chen@intel.com>
> ---
>  arch/x86/kernel/kvmclock.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/kvmclock.c b/arch/x86/kernel/kvmclock.c
> index d9156ce..0bf3467 100644
> --- a/arch/x86/kernel/kvmclock.c
> +++ b/arch/x86/kernel/kvmclock.c
> @@ -59,13 +59,12 @@ static void kvm_get_wallclock(struct timespec *now)
>  
>  	native_write_msr(msr_kvm_wall_clock, low, high);
>  
> -	preempt_disable();
> -	cpu = smp_processor_id();
> +	cpu = get_cpu();
>  
>  	vcpu_time = &hv_clock[cpu].pvti;
>  	pvclock_read_wallclock(&wall_clock, vcpu_time, now);
>  
> -	preempt_enable();
> +	put_cpu();
>  }
>  
>  static int kvm_set_wallclock(const struct timespec *now)
> @@ -107,11 +106,10 @@ static unsigned long kvm_get_tsc_khz(void)
>  	int cpu;
>  	unsigned long tsc_khz;
>  
> -	preempt_disable();
> -	cpu = smp_processor_id();
> +	cpu = get_cpu();
>  	src = &hv_clock[cpu].pvti;
>  	tsc_khz = pvclock_tsc_khz(src);
> -	preempt_enable();
> +	put_cpu();
>  	return tsc_khz;
>  }
>  
> @@ -284,23 +282,22 @@ int __init kvm_setup_vsyscall_timeinfo(void)
>  
>  	size = PAGE_ALIGN(sizeof(struct pvclock_vsyscall_time_info)*NR_CPUS);
>  
> -	preempt_disable();
> -	cpu = smp_processor_id();
> +	cpu = get_cpu();
>  
>  	vcpu_time = &hv_clock[cpu].pvti;
>  	flags = pvclock_read_flags(vcpu_time);
>  
>  	if (!(flags & PVCLOCK_TSC_STABLE_BIT)) {
> -		preempt_enable();
> +		put_cpu();
>  		return 1;
>  	}
>  
>  	if ((ret = pvclock_init_vsyscall(hv_clock, size))) {
> -		preempt_enable();
> +		put_cpu();
>  		return ret;
>  	}
>  
> -	preempt_enable();
> +	put_cpu();
>  
>  	kvm_clock.archdata.vclock_mode = VCLOCK_PVCLOCK;
>  #endif
> 

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>

but will wait for 3.19.

Paolo