detecting hyperthreading

[Gary Jennejohn]

On Tue, 10 Mar 2015 10:07:19 -0600
Alan Somers <asomers at freebsd.org> wrote:

> On Tue, Mar 10, 2015 at 10:02 AM, Freddie Cash <fjwcash at gmail.com> wrote:
> > On Tue, Mar 10, 2015 at 8:56 AM, Pokala, Ravi <rpokala at panasas.com> wrote:
> >
> >> -----Original Message-----
> >> From: "lokadamus at gmx.de" <lokadamus at gmx.de>
> >> Date: 2015-03-10, Tuesday at 08:52
> >> To: Ravi Pokala <rpokala at panasas.com>, Rui Paulo <rpaulo at me.com>
> >> Cc: "freebsd-hackers at freebsd.org" <freebsd-hackers at freebsd.org>
> >> Subject: Re: detecting hyperthreading
> >>
> >> >Have you look at dmesg?
> >> >My system is a P4 with HTT.
> >> >dmesg |more
> >> [...]
> >> >CPU: Intel(R) Pentium(R) 4 CPU 3.00GHz (3000.00-MHz 686-class CPU)
> >> >  Origin = "GenuineIntel"  Id = 0xf29  Family = 0xf  Model = 0x2
> >> >Stepping = 9
> >> >
> >> >Features=0xbfebfbff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,APIC,SEP,MTRR,PGE,M
> >> >CA,CMOV,PAT,PSE36,CLFLUSH,DTS,ACPI,MMX,FXSR,SSE,SSE2,SS,HTT,TM,PBE>
> >> >  Features2=0x4400<CNXT-ID,xTPR>
> >>
> >> Of course. :-)
> >>
> >> But there are two problems:
> >>
> >> (1) That just tells me HTT is supported by the CPU, not that if kernel is
> >> using it.
> >> (2) It's difficult to parse.
> >>
> >> Of the two, (1) is the bigger concern for my use-case.
> >>
> >
> > 6 lines or so below the Features line shows the kernel loading "cpu0
> > (BSP)", and then "cpu1 (AP/HT)".
> >
> > Compare that to a system without HTT, where any extra cpus only show "(AP)".
> >
> > It's not perfect, but one could grep through /var/run/dmesg.boot looking
> > for "cpu" lines and checking for "(AP)" or "(AP/HT)".
> >
> > --
> > Freddie Cash
> > fjwcash at gmail.com
> 
> I always look at "sysctl kern.sched.topology_spec" to tell if
> hyperthreading is enabled.  It's overkill, but it works.
>
[snip Ruby]

Is this ULE-specific?  This OID isn't present on my box using the
BSD scheduler.  Something to be aware of.

-- 
Gary Jennejohn