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CaptainBlood
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PostPosted: Sun Feb 15, 2015 6:52 pm    Post subject: How 2 switch kernel CPU mode between Threaded / UnThreaded Reply with quote

Hi,

Should I achieve this with 2 differents .config?
Or should kernel command line suffices?
I expect "UnThreaded" to be time saving while emerging single threaded ebuilds.

Thks 4 ur attention


Last edited by CaptainBlood on Sun Feb 15, 2015 8:37 pm; edited 1 time in total
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Ant P.
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PostPosted: Sun Feb 15, 2015 7:58 pm    Post subject: Reply with quote

Your expectations are broken, unless you plan to run that emerge as the init process on a machine with no consoles or background processes at all.
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CaptainBlood
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PostPosted: Sun Feb 15, 2015 8:50 pm    Post subject: Reply with quote

Thks for advice... :oops:

Anyhow the question remains:
Is it possible to configure kernel (via .config or command line) so that the 2 cores are taken into account, and that each core isn't splitted into 2 logical ones?

Thks 4 ur attention, interest & support
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NeddySeagoon
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PostPosted: Sun Feb 15, 2015 9:57 pm    Post subject: Reply with quote

CaptainBlood,

Turn off Hyperthreading support in the BIOS and in the kernel.

I don't see a command line option in /usr/src/linux/Documentation/kernel-parameters.txt
Maybe there is something in the kernel help?
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CaptainBlood
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PostPosted: Tue Feb 17, 2015 9:07 pm    Post subject: Reply with quote

NeddySeagoon wrote:
CaptainBlood,

Turn off Hyperthreading support in the BIOS and in the kernel.

I don't see a command line option in /usr/src/linux/Documentation/kernel-parameters.txt
Maybe there is something in the kernel help?


My laptop hasn't got such a setting.
Seems like there is no setting in kernel .config, but replacement of the CPU embeded hyperthreading scheduler.

Thks 4 ur attention, interest & support.
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Yamakuzure
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PostPosted: Wed Feb 18, 2015 10:32 am    Post subject: Reply with quote

BIOS: Here you can (normally) set whether HyperThreading is supported or not. To use it, it must be enabled.
Kernel: Either build with the SMT Scheduler (CONFIG_SCHED_SMT) or not.

Disabling the SMT-Scheduler disables HyperThreading, no matter what you have set in your BIOS.
Enabling the SMT-Scheduler without enabling support in the BIOS only adds overhead.

On my laptop (i7, 4 cores) the overall performance is worse without HyperThreading. Nowadays it is a too rare occasion that a single process hogs only one logical CPU for disabling HyperThreading to give me any benefit.
This might, of course, be completely different on your setup.
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CaptainBlood
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PostPosted: Tue Mar 31, 2015 7:50 pm    Post subject: Reply with quote

Hi,
No such an option in laptop BIOS.

So seems like there are little chances to have dual core cpu involved without each being splited into 2 logical CPUs.

While doing
Quote:
emerge -e word
I've noticed many single threaded phases.

This is why I'm trying so hard to have system to work with the 2 physical CPUs.


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s4e8
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PostPosted: Tue Apr 07, 2015 3:12 pm    Post subject: Reply with quote

just add kernel param maxcpus=<half_of_#cpu>, it only work on single cpu package or some 2way server.
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CaptainBlood
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PostPosted: Tue Apr 07, 2015 6:21 pm    Post subject: Reply with quote

Yes that's an issue, only 1 CPU until next reboot.
Not an option, sorry. :wink:

Quote:
some 2way server
What do you mean?

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CaptainBlood
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PostPosted: Tue Apr 07, 2015 6:37 pm    Post subject: Reply with quote

Yamakuzure wrote:
Enabling the SMT-Scheduler without enabling support in the BIOS only adds overhead.
should be the way...
Let me think it over, & I'll get back 4 more results.
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s4e8
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PostPosted: Wed Apr 08, 2015 8:16 am    Post subject: Reply with quote

On single CPU system, logical cpus always sorted by coreid threadid, ie: all physical cores at first, threaded-cpus next.
On two CPU system, some m/b sorted by coreid socketid threadid and others by coreid threadid socketid. First method upper half cpus is threaded, but second method, upper half cpus is second socket's.
CaptainBlood wrote:

Quote:
some 2way server
What do you mean?
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