From: Peter Zijlstra <peterz@infradead.org>
To: Uladzislau Rezki <urezki@gmail.com>
Cc: 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)
Date: Fri, 3 Jul 2020 19:38:14 +0200 [thread overview]
Message-ID: <20200703173814.GZ4800@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20200703170941.GA4372@pc636>
On Fri, Jul 03, 2020 at 07:09:41PM +0200, Uladzislau Rezki wrote:
> 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.
Nah, it's based on ACPI (SRAT IIRC) tables. The case of
over-provisioning is useful for systems that support physical hotplug,
but I've seen boards without that capability do it too.
Just chalk it up to the foibles of BIOS.
next prev parent reply other threads:[~2020-07-03 17:38 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-03 15:57 nr_cpu_ids vs AMD 3970x(32 physical CPUs) Uladzislau Rezki
2020-07-03 16:56 ` Peter Zijlstra
2020-07-03 17:09 ` Uladzislau Rezki
2020-07-03 17:38 ` Peter Zijlstra [this message]
2020-07-03 19:26 ` Uladzislau Rezki
2020-07-03 17:07 ` Gabriel C
2020-07-03 17:24 ` Uladzislau Rezki
2020-07-03 17:45 ` Peter Zijlstra
2020-07-03 18:36 ` Gabriel C
2020-07-03 19:05 ` peter enderborg
2020-07-03 19:28 ` Uladzislau Rezki
2020-07-03 20:08 ` Linus Torvalds
2020-07-03 21:20 ` Uladzislau Rezki
2020-07-03 21:51 ` Matthew Wilcox
2020-07-03 22:22 ` Uladzislau Rezki
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