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SubjectRe: [PATCH RFC] x86: fix confusing name of /proc/cpuinfo "ht" flag

* H. Peter Anvin <hpa@zytor.com> wrote:

> On 11/11/2009 10:59 PM, Ingo Molnar wrote:
> >
> > * Bartlomiej Zolnierkiewicz <bzolnier@gmail.com> wrote:
> >
> >> "ht" flag indicates only ability to detect siblings not HT presence
> >> itself.
> >>
> >> Inspired by:
> >> http://www.codemonkey.org.uk/2009/11/10/common-hyperthreading-misconception/
> >
> > i think instead of changing 'ht' to 'ht_detect', it would be even
> > more intuitive to only expose the 'ht' flag if the ht-detect
> > capability is there _and_ if the number of siblings is 2 or more.
> >
> > That way we dont change it - we just 'hide' the 'ht' string on the
> > category of systems that can enumerate HT via the CPUID but dont
> > actually have HyperThreading.
>
> /proc/cpuinfo is a user-space visible ABI. Changing it is bad
> chicken.

Almost ... something is only an ABI if an actual application relies on
the 'ht' flag being there on non-hyperthreading CPUs. We dont know
whether there's any, but the likelyhood looks pretty low. Could park it
a branch for some time to see whether anything trips up.

Ingo


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