linux-kernel - Re: [PATCH 1/2] kvm: x86: add likely to sched_info

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Date:   Thu, 4 Jul 2019 14:15:12 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yi Wang <wang.yi59@....com.cn>
Cc:     rkrcmar@...hat.com, tglx@...utronix.de, mingo@...hat.com,
        bp@...en8.de, hpa@...or.com, x86@...nel.org, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        xue.zhihong@....com.cn, up2wing@...il.com, wang.liang82@....com.cn
Subject: Re: [PATCH 1/2] kvm: x86: add likely to sched_info_on()

On 04/07/19 13:46, Yi Wang wrote:
> The condition to test is likely() to be true when make defconfig.
> Add the hint.
> 
> Signed-off-by: Yi Wang <wang.yi59@....com.cn>
> ---
>  arch/x86/kvm/cpuid.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 4992e7c..64fff41 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -642,7 +642,7 @@ static inline int __do_cpuid_ent(struct kvm_cpuid_entry2 *entry, u32 function,
>  			     (1 << KVM_FEATURE_ASYNC_PF_VMEXIT) |
>  			     (1 << KVM_FEATURE_PV_SEND_IPI);
>  
> -		if (sched_info_on())
> +		if (likely(sched_info_on()))
>  			entry->eax |= (1 << KVM_FEATURE_STEAL_TIME);

This is not a fast path, so adding likely/unlikely is unnecessary.

Paolo

>  		entry->ebx = 0;
>