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From:   Uladzislau Rezki <urezki@gmail.com>
Date:   Fri, 3 Jul 2020 19:09:41 +0200
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     Uladzislau Rezki <urezki@gmail.com>, linux-kernel@vger.kernel.org,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        GregKroah-Hartmangregkh@linuxfoundation.org
Subject: Re: nr_cpu_ids vs AMD 3970x(32 physical CPUs)
Message-ID: <20200703170941.GA4372@pc636>
References: <20200703155749.GA6255@pc636>
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On Fri, Jul 03, 2020 at 06:56:27PM +0200, Peter Zijlstra wrote:
> On Fri, Jul 03, 2020 at 05:57:49PM +0200, Uladzislau Rezki wrote:
> > Hello, folk.
> > 
> > I have a system based on AMD 3970x CPUs. It has 32 physical cores
> > and 64 threads. It seems that "nr_cpu_ids" variable is not correctly
> > set on latest 5.8-rc3 kernel. Please have a look below on dmesg output:
> > 
> > <snip>
> > urezki@pc638:~$ sudo dmesg | grep 128
> > [    0.000000] IOAPIC[0]: apic_id 128, version 33, address 0xfec00000, GSI 0-23
> > [    0.000000] smpboot: Allowing 128 CPUs, 64 hotplug CPUs
> 
> This is your BIOS saying it needs 128 ids, 64 of which are 'empty'.
> 
> I have a box like that as well, if it bothers you boot with:
> "possible_cpus=64" or something.
>
OK, i got it. I thought that "cpu_possible_mask" strictly follows
the rule: the number of CPUs in a system that physically are present.

Thanks, Peter!

--
Vlad Rezki