Hyperthreading vs performance

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meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Hyperthreading vs performance

Post by meteoadriatic » Sun Mar 02, 2014 5:22 pm

Hello,

has anybody done benchmark tests on Intel i7 quadcores, with/without Hyperthreading, and has results handy? I have i7 3770 based computer in remote datacenter with HT enabled (of course), and it will be little bit of pain requesting KVM access to disable it, so if there is no big difference I would rather leave it as is. Any experiences?

oib
Posts: 117
Joined: Mon Jan 31, 2011 3:29 pm

Re: Hyperthreading vs performance

Post by oib » Tue Mar 04, 2014 8:30 am

No experience with Intel i7.
I can tell you that on a 2 x Intel Xeon E3 2697v2 the run results 33% faster without HyperThreading.

meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Re: Hyperthreading vs performance

Post by meteoadriatic » Tue Mar 04, 2014 9:02 pm

Thx.

Found that HT can be disabled in linux. Just add maxcpus=4 to kernel boot line in grub.conf, so I'll test with that first:
http://www.bitsecure.com/disabling-hype ... entosrhel/
Last edited by meteoadriatic on Wed Mar 05, 2014 2:07 pm, edited 1 time in total.

meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Re: Hyperthreading vs performance

Post by meteoadriatic » Wed Mar 05, 2014 11:24 am

Just tested and works very well. In fact this is more elegant way to turn HT off than doing that in BIOS. Results for my custom test are:

HT on: 31min 28s
HT off: 27min 07s

(about 16% difference for this configuration)

oib
Posts: 117
Joined: Mon Jan 31, 2011 3:29 pm

Re: Hyperthreading vs performance

Post by oib » Wed Mar 05, 2014 1:32 pm

meteoadriatic wrote:Thx.

Found that HT can be disabled in linux. Just add maxcpus=8 to kernel boot line in grub.conf, so I'll test with that first:
http://www.bitsecure.com/disabling-hype ... entosrhel/
Great!
You are always able to find a solution ;)

Gippox
Posts: 59
Joined: Sat Mar 02, 2013 1:16 am

Re: Hyperthreading vs performance

Post by Gippox » Tue Mar 25, 2014 8:47 pm

Hi Meteo,
i have i7 4770k, with HT enabled (Fedora 20), but for WRF-EMS 3.4 i use in ems.cshrc
setenv NCPUS 1
setenv CORES 4
in ems.profile
NCPUS=1 ; export NCPUS
CORES=4 ; export CORES
in run_ncpus.conf
REAL_NODECPUS = local:4
WRFM_NODECPUS = local:4

I think it is the same thing as having the HT off from bios, in fact if i use all the 8-core WRF is slower (10-15%)

Gippox

meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Re: Hyperthreading vs performance

Post by meteoadriatic » Tue Mar 25, 2014 9:30 pm

Interesting. Are you sure that you use all CPU resources with that configuration? What htop say?

Gippox
Posts: 59
Joined: Sat Mar 02, 2013 1:16 am

Re: Hyperthreading vs performance

Post by Gippox » Tue Mar 25, 2014 9:56 pm

Htop show 4 cores working at 100% (wrfm_arw.exe) and 4 cores at 5-45% (depending on what i use in the operating system)

meteoadriatic
Posts: 1510
Joined: Wed Aug 19, 2009 10:05 am

Re: Hyperthreading vs performance

Post by meteoadriatic » Wed Mar 26, 2014 7:18 am

And what is performance if you use 6 or 7 threads? Is it better?

Gippox
Posts: 59
Joined: Sat Mar 02, 2013 1:16 am

Re: Hyperthreading vs performance

Post by Gippox » Fri Mar 28, 2014 5:14 pm

Hi did some quick test :mrgreen: :

1) HT off (BIOS): 10 min 4 sec
2) HT on 4 thread : 10 min 8 sec
3) HT on 6 thread : 10 min 44 sec
4) HT on 7 thread : 10 min 46 sec

The solutions number 1 and 2 are identical for performance, 3-4 are 6% slower.

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