Re: [PATCH] x86: reduce redundancy in tsc_[gs]et_info()

[Boris Ostrovsky <boris.ostrovsky@oracle.com>]

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On 04/30/2014 09:53 AM, Jan Beulich wrote:
> - some of the case statements are effectively or mostly special cases
>    of others, so there's no good reason not to share the code
> - in the "get" function, a variable can be made case-wide instead of
>    having multiple instance of it (and those even with a pointless
>    initializer)
> - minor formatting adjustments
>
> Signed-off-by: Jan Beulich <jbeulich@suse.com>

Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>

>
> --- a/xen/arch/x86/time.c
> +++ b/xen/arch/x86/time.c
> @@ -1786,26 +1786,22 @@ void tsc_get_info(struct domain *d, uint
>   
>       switch ( *tsc_mode )
>       {
> +        uint64_t tsc;
> +
>       case TSC_MODE_NEVER_EMULATE:
> -        *elapsed_nsec =  *gtsc_khz = 0;
> +        *elapsed_nsec = *gtsc_khz = 0;
>           break;
> -    case TSC_MODE_ALWAYS_EMULATE:
> -        *elapsed_nsec = get_s_time() - d->arch.vtsc_offset;
> -        *gtsc_khz =  d->arch.tsc_khz;
> -         break;
>       case TSC_MODE_DEFAULT:
>           if ( d->arch.vtsc )
>           {
> +    case TSC_MODE_ALWAYS_EMULATE:
>               *elapsed_nsec = get_s_time() - d->arch.vtsc_offset;
>               *gtsc_khz =  d->arch.tsc_khz;
> +            break;
>           }
> -        else
> -        {
> -            uint64_t tsc = 0;
> -            rdtscll(tsc);
> -            *elapsed_nsec = scale_delta(tsc,&d->arch.vtsc_to_ns);
> -            *gtsc_khz =  cpu_khz;
> -        }
> +        rdtscll(tsc);
> +        *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns);
> +        *gtsc_khz =  cpu_khz;
>           break;
>       case TSC_MODE_PVRDTSCP:
>           if ( d->arch.vtsc )
> @@ -1815,10 +1811,9 @@ void tsc_get_info(struct domain *d, uint
>           }
>           else
>           {
> -            uint64_t tsc = 0;
>               rdtscll(tsc);
> -            *elapsed_nsec = (scale_delta(tsc,&d->arch.vtsc_to_ns) -
> -                             d->arch.vtsc_offset);
> +            *elapsed_nsec = scale_delta(tsc, &d->arch.vtsc_to_ns) -
> +                            d->arch.vtsc_offset;
>               *gtsc_khz = 0; /* ignored by tsc_set_info */
>           }
>           break;
> @@ -1875,28 +1870,24 @@ void tsc_set_info(struct domain *d,
>   
>       switch ( d->arch.tsc_mode = tsc_mode )
>       {
> -    case TSC_MODE_NEVER_EMULATE:
> -        d->arch.vtsc = 0;
> -        break;
> -    case TSC_MODE_ALWAYS_EMULATE:
> -        d->arch.vtsc = 1;
> -        d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
> -        d->arch.tsc_khz = gtsc_khz ? gtsc_khz : cpu_khz;
> -        set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
> -        d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
> -        break;
>       case TSC_MODE_DEFAULT:
> -        d->arch.vtsc = 1;
> +    case TSC_MODE_ALWAYS_EMULATE:
>           d->arch.vtsc_offset = get_s_time() - elapsed_nsec;
> -        d->arch.tsc_khz = gtsc_khz ? gtsc_khz : cpu_khz;
> -        set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000 );
> -        /* use native TSC if initial host has safe TSC, has not migrated
> -         * yet and tsc_khz == cpu_khz */
> -        if ( host_tsc_is_safe() && incarnation == 0 &&
> -                d->arch.tsc_khz == cpu_khz )
> +        d->arch.tsc_khz = gtsc_khz ?: cpu_khz;
> +        set_time_scale(&d->arch.vtsc_to_ns, d->arch.tsc_khz * 1000);
> +        /*
> +         * In default mode use native TSC if the host has safe TSC,
> +         * the VM has not migrated yet, and tsc_khz == cpu_khz.
> +         */
> +        if ( tsc_mode == TSC_MODE_DEFAULT && host_tsc_is_safe() &&
> +             incarnation == 0 && d->arch.tsc_khz == cpu_khz )
> +        {
> +    case TSC_MODE_NEVER_EMULATE:
>               d->arch.vtsc = 0;
> -        else
> -            d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
> +            break;
> +        }
> +        d->arch.vtsc = 1;
> +        d->arch.ns_to_vtsc = scale_reciprocal(d->arch.vtsc_to_ns);
>           break;
>       case TSC_MODE_PVRDTSCP:
>           d->arch.vtsc =  boot_cpu_has(X86_FEATURE_RDTSCP) &&
>
>
>
>
>
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