[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] x86/time: Don't use virtual TSC if host and guest frequencies are equal
>>> On 16.03.17 at 15:22, <boris.ostrovsky@xxxxxxxxxx> wrote: > On 03/16/2017 09:31 AM, Jan Beulich wrote: >>>>> On 16.03.17 at 13:44, <boris.ostrovsky@xxxxxxxxxx> wrote: >>> On 03/16/2017 06:40 AM, Jan Beulich wrote: >>>>>>> On 15.03.17 at 20:48, <boris.ostrovsky@xxxxxxxxxx> wrote: >>>>> --- a/xen/arch/x86/time.c >>>>> +++ b/xen/arch/x86/time.c >>>>> @@ -2051,17 +2051,11 @@ void tsc_set_info(struct domain *d, >>>>> d->arch.vtsc_offset = get_s_time() - elapsed_nsec; >>>>> 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 and: >>>>> - * HVM/PVH: host and guest frequencies are the same (either >>>>> - * "naturally" or via TSC scaling) >>>>> - * PV: guest has not migrated yet (and thus arch.tsc_khz == > cpu_khz) >>>>> - */ >>>>> + >>>>> if ( tsc_mode == TSC_MODE_DEFAULT && host_tsc_is_safe() && >>>>> - (has_hvm_container_domain(d) ? >>>>> - (d->arch.tsc_khz == cpu_khz || >>>>> - hvm_get_tsc_scaling_ratio(d->arch.tsc_khz)) : >>>>> - incarnation == 0) ) >>>>> + (d->arch.tsc_khz == cpu_khz || incarnation == 0 || >>>> Is the incarnation comparison really needed here, i.e. doesn't it >>>> being zero imply the two frequencies to match in default mode? >>> It is not necessary but I wanted to keep it for clarity so that it is >>> explicit that when a domain is born we don't use vtsc. >> Well, considering the history here, I think its presence is rather >> going to raise questions than to answer any, so if anything I'd >> suggest to have an ASSERT() to that effect, at once serving as >> sort of documentation. But I may be the only one thinking this >> way ... > > > Haven't thought about an ASSERT. I can do that. Something like > > ASSERT(gtsc_khz == 0 ? incarnation == 0 : true); ASSERT(incarnation || d->arch.tsc_khz == cpu_khz); Jan _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx https://lists.xen.org/xen-devel
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