detecting hyperthreading

[Freddie Cash]

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