Ok let me expand then. I don't have control over the bios.
The testing I am doing resides on a cloud provider and from our testing it
appears that it has HT enabled. It is ambiguous though to me what I see vs how
they allocate on their hypervisor.
I want to see if this has any effect. given the providers advertised CPU types
they use vs my bare metal ones of the same types everything feels 'half as
fast' Thus the question about HT.
Here is the lstopo from the provider:
lstopo-no-graphics
Machine (7484MB)
Socket L#0 + L3 L#0 (25MB)
L2 L#0 (256KB) + L1d L#0 (32KB) + L1i L#0 (32KB) + Core L#0
PU L#0 (P#0)
PU L#1 (P#2)
L2 L#1 (256KB) + L1d L#1 (32KB) + L1i L#1 (32KB) + Core L#1
PU L#2 (P#1)
PU L#3 (P#3)
HostBridge L#0
PCI 8086:7010
PCI 1013:00b8
PCI 8086:10ed
Net L#0 "eth0"
Brock Palen
www.umich.edu/~brockp
CAEN Advanced Computing
XSEDE Campus Champion
bro...@umich.edu
(734)936-1985
> On Dec 11, 2014, at 4:12 PM, Jeff Squyres (jsquyres) <jsquy...@cisco.com>
> wrote:
>
> I'm not sure you're asking a well-formed question.
>
> When the BIOS is set to enable hyper threading, then several resources on the
> core are split when the machine is booted up (e.g., some of the queue depths
> for various processing units in the core are half the length that they are
> when hyperthreading is disabled in the BIOS).
>
> Hence, running a process on a core that only uses a single hyperthread (when
> HT is enabled) is not quite the same thing as booting up with HT disabled and
> running that same job on the core.
>
> Make sense?
>
> Meaning: if you want to test HT vs. non-HT performance, you really need to
> change the BIOS settings and reboot, sorry.
>
> Also, note that if you have HT enabled and you run a single-threaded app
> bound to a core, it will only use 1 of those HTs -- the other HT will be
> largely dormant. Meaning: don't expect that running a single-threaded app on
> a core that has HT enabled will magically take advantage of some performance
> benefit of aggressive automatic parallelization. You really need multiple
> threads in a process to get performance advantages out of HT.
>
>
>
> On Dec 11, 2014, at 12:51 PM, Brock Palen <bro...@umich.edu> wrote:
>
>> When a system has HT enabled is one core presented the real one and one the
>> fake partner? Or is that not the case?
>>
>> If wanting to test behavior without messing with the bios how do I select
>> just the 'real cores' if this is the case?
>>
>> I am looking for the equivelent of
>>
>> hwloc-bind ALLREALCORES my.exe
>>
>> Doing some performance study type things.
>>
>> Thanks,
>>
>> Brock Palen
>> www.umich.edu/~brockp
>> CAEN Advanced Computing
>> XSEDE Campus Champion
>> bro...@umich.edu
>> (734)936-1985
>>
>>
>>
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>> Link to this post:
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>
>
> --
> Jeff Squyres
> jsquy...@cisco.com
> For corporate legal information go to:
> http://www.cisco.com/web/about/doing_business/legal/cri/
>
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