linux-kernel - Re: [PATCH linux-next] KVM: selftests: remove redundant variable tsc

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Date:   Wed, 31 Aug 2022 09:17:14 -0700
From:   Jim Mattson <jmattson@...gle.com>
To:     cgel.zte@...il.com
Cc:     pbonzini@...hat.com, shuah@...nel.org, seanjc@...gle.com,
        dmatlack@...gle.com, peterx@...hat.com, oupton@...gle.com,
        kvm@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Jinpeng Cui <cui.jinpeng2@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH linux-next] KVM: selftests: remove redundant variable tsc_val

On Wed, Aug 31, 2022 at 7:31 AM <cgel.zte@...il.com> wrote:
>
> From: Jinpeng Cui <cui.jinpeng2@....com.cn>
>
> Return value directly from expression instead of
> getting value from redundant variable tsc_val.

Nit: I think you mean 'superfluous' rather than 'redundant'?

> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Jinpeng Cui <cui.jinpeng2@....com.cn>
> ---
>  tools/testing/selftests/kvm/include/x86_64/processor.h | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
> index 0cbc71b7af50..75920678f34d 100644
> --- a/tools/testing/selftests/kvm/include/x86_64/processor.h
> +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
> @@ -237,7 +237,6 @@ static inline uint64_t get_desc64_base(const struct desc64 *desc)
>  static inline uint64_t rdtsc(void)
>  {
>         uint32_t eax, edx;
> -       uint64_t tsc_val;
>         /*
>          * The lfence is to wait (on Intel CPUs) until all previous
>          * instructions have been executed. If software requires RDTSC to be
> @@ -245,8 +244,8 @@ static inline uint64_t rdtsc(void)
>          * execute LFENCE immediately after RDTSC
>          */
>         __asm__ __volatile__("lfence; rdtsc; lfence" : "=a"(eax), "=d"(edx));
> -       tsc_val = ((uint64_t)edx) << 32 | eax;
> -       return tsc_val;
> +
> +       return ((uint64_t)edx) << 32 | eax;
>  }

This does beg the question: "Why?"