Re: [Xen-devel] [PATCH v4 1/3] x86: Use native RDTSC(P) execution when guest and host frequencies are the same

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.04.14 at 03:27, <boris.ostrovsky@xxxxxxxxxx> wrote:
> @@ -1889,10 +1890,14 @@ void tsc_set_info(struct domain *d,
>          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 )
> +        /*
> +         * Use native TSC if initial host has safe TSC and either has not
> +         * migrated yet or tsc_khz == cpu_khz (either "naturally" or via
> +         * TSC scaling)
> +         */
> +        if ( host_tsc_is_safe() &&
> +             (incarnation == 0 || d->arch.tsc_khz == cpu_khz ||
> +              cpu_has_tsc_ratio) )

Can't you drop checking incarnation to be zero then? In that case,
afaict d->arch.tsc_khz == cpu_khz due to gtsc_khz being passed
in as zero from arch_domain_create().

Jan


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