Maximum Core Count on 32 bit systems

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mdamda
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Maximum Core Count on 32 bit systems

Post by mdamda » 2018/03/20 06:58:22

Hello all,

I'm currently running a bunch of apps on a group of Centos 5 / Red Hat 5 systems.

Unfortunately these apps are no longer updated to support 64 bit OSes. I'm looking to move to Centos 6 in the meantime, but still 32bit.

If we move to a machine with more than 32 logical cores, what would be the default behavior of the OS? I understand that 32bit Centos/RHEL has a maximum core count of 32 for 32bit systems...
Will the hardware...
a) Reject the OS install?
b) See only 32 threads -- in this case, which threads are "seen" first? The real cores or the SMT/HT ones?

Looking to scope out a server, not sure if I should get the one with 32 cores or 40...

Thanks!
Last edited by mdamda on 2018/03/20 07:40:25, edited 1 time in total.

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avij
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Re: Maximum Core Count on 32 bit systems

Post by avij » 2018/03/20 07:30:53

Unfortunately I don't have a >32 core server to play with, but my educated guess is that the "a" option is out. Those who have better information, please speak out.

Depending on your use case, you could also consider running a newer operating system (such as CentOS 7) as a virtualization host, and run your CentOS 6 installations as virtual machines. The host could use all CPU cores, even if each individual 32bit CentOS 6 VM is restricted to 32 cores.

mdamda
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Re: Maximum Core Count on 32 bit systems

Post by mdamda » 2018/03/20 07:39:07

Thanks for this.

The reason for this post is that we're about to purchase a server, and an additional 4 cores and 8 threads are just 500$ away. Just don't want to be throwing away that money if option a indeed happens :mrgreen: :mrgreen:

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TrevorH
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Re: Maximum Core Count on 32 bit systems

Post by TrevorH » 2018/03/20 14:12:06

The documented limits for the upstream releases is here but that won't really help since there is no 32 bit RHEL 7. though it does confirm that el6 32 bit has a 32 core limit. No idea what will happen if you try to boot 32 bit el6 on say a 40 core machine but I would think that if it boots at all then it's likely to show you cores 0-31 whether those are HT or not.
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tunk
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Re: Maximum Core Count on 32 bit systems

Post by tunk » 2018/03/20 16:10:19

Are you sure it won't work with CentOS 64 bit together with its 32 bit compatibility libraries?

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TrevorH
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Re: Maximum Core Count on 32 bit systems

Post by TrevorH » 2018/03/20 16:19:20

Yes, I agree, 64 bit CentOS can easily run 32 bit apps without them even knowing.
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mdamda
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Re: Maximum Core Count on 32 bit systems

Post by mdamda » 2018/03/21 02:17:41

We are certainly willing to try... but just in case it doesn't work out, I don't want to be left with an expensive box that can't do what we need it to! :D :D

Whoever
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Re: Maximum Core Count on 32 bit systems

Post by Whoever » 2018/03/21 04:46:11

mdamda wrote:We are certainly willing to try... but just in case it doesn't work out, I don't want to be left with an expensive box that can't do what we need it to! :D :D
As avij pointed out, it may be best to install CentOS 7/64 bit and run CentOS 6 guests.

You can definitely run 32-bit apps on 64-bit systems, but you may need to install some packages. Start with this instruction from Trevor in an older post:

Code: Select all

yum install glibc.i686
For a larger set of 32-bit packages, you can try:

Code: Select all

yum install libstdc++.i686

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avij
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Re: Maximum Core Count on 32 bit systems

Post by avij » 2018/03/21 07:27:38

I'll just echo that installing CentOS 6 x86_64 and running your 32bit apps in it is also a good suggestion.

tunk
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Re: Maximum Core Count on 32 bit systems

Post by tunk » 2018/03/21 12:59:46

Would it be possible to test it beforehand on an old 64bit desktop/laptop? And why not go for CentOS 7?

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