Re: [gentoo-user] RYZEN 5: Hyperthreading or no hyperthreading...

[Mark Knecht]

On Fri, Mar 27, 2020 at 10:58 PM <tuxic@××××××.de> wrote:
>
> On 03/27 11:51, Mark Knecht wrote:
> > On Fri, Mar 27, 2020 at 11:11 AM <tuxic@××××××.de> wrote:
> > >
> > > On 03/27 06:04, Andrea Conti wrote:
> > > > Hello,
> > > >
> > > > > Thread(s) per core:              1 <<<<<
> > > > > Does my CPU hyperthread?
> > > >
> > > > Definitely not.
> > > >
> > > > Your kernel config is fine, chances are hyperthreading (aka "SMT
mode")
> > is
> > > > disabled in your BIOS settings.
> > > >
> > > > andrea
> > > >
> > >
> > > Hi Andrea,
> > >
> > > I checked that: The BIOS setting was set to use hyperthreading.
> > >
> > > But "Number of cores" was set to six. I changed that to 12 and
> > > Voila! I got two threads per core.
> > >
> > > I think "Number of cores" is a little misleading, since there
> > > are six physical cores (not threads) with a RYZEN 5.
> > >
> > > I feeling not that comfortable with this solution.
> > >
> > > Is there any way to check for the validity of this setting
> > > beside a tool, which prints a "2" after the word "threads" ;) ?
> > >
> > > Cheers!
> > > Meino
> > >
> > >
> >
> > cat /proc/cpu should give info for each thread. I've been running an i7
980
> > Extreme processor @3.33GHz here at home for about 12 years or so. It's 6
> > cores but shows 12 processors on both Gentoo and now Kubuntu.
> >
> > I generally run top and then hit '1' and 'z'. You can watch what
percentage
> > each core/thread is using.
> >
> > Time a BIG compile job twice, once with each kernel. If it's working
you'll
> > measure a significant difference in time. Note that it won't be 2x as
> > you'll also be limited by disk read/write throughput, but you'll know
it's
> > basically working.
> >
> > On Gentoo make sure you're compile settings in (I think make.conf - I no
> > longer run Gentoo much) are set to take advantage of all your cores and
not
> > limited to something smaller. Also watch overheating when using more
> > cores/threads. On older PCs like mine when you possibly have dust in CPU
> > coolers might not be as efficient as when they are new.
> >
> > HTH,
> > Mark
>
> Hi Mark,
>
> thank you for your explanations! :)
>
> /proc/cpu doesn't exist on my system....may be you are referring to
> /proc/cpuinfo?
>
> The problem was caused by a kernel misconfiguration by me.
>
> In the kernel setup there is a setting "Number of cores" which
> I had set to six ... since my CPU has 6 physical core.
>
> Setting this to twelve (and blurring the syntactically border between
> threads and cores thereby...) gives me twelves cores in top, htop
> and such and (as an example) compiling the kernel is faster -
> so it is not a display gimmick only.
>
> I think "Number of cores" is a misnomer...or am I wrong?
>
> Cheers!
> Meino
>

Meino,
   Yes, /proc/cpuinfo. Sorry.

   Well yes, I guess the 'Number of cores' is a misnomer if you're trying
to equate the language in the kernel against Intel/AMD marketing data for
physical cores. 6 physical cores with or without hyperthreading is still 6
physical cores. However 6 physical cores (my processor) _WITH_
hyperthreading enabled is 12 _LOGICAL_ cores which is more what I think the
kernel verbiage is about. Semantics I suppose.

   I'm glad you found it wasn't a gimmicky number. It really does work,
within the limits of the hardware being able to figure out what one thread
should be fetching or writing while the other thread is computing. It's not
a perfect 2:1 like 12 physical cores might be, but it's a lot less silicon
and therefore a lot less expensive.

Cheers,
Mark