linux-kernel - Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 12 Jan 2010 14:20:22 -0800
From:	Yinghai Lu <yinghai@...nel.org>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Suresh Siddha <suresh.b.siddha@...el.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/5] use nr_cpus= to set nr_cpu_ids early

On Tue, Jan 12, 2010 at 12:31 PM, Christoph Lameter
<cl@...ux-foundation.org> wrote:
> On Tue, 12 Jan 2010, Yinghai Lu wrote:
>
>> > Why do we need this twice?
>>
>> maxcpus only change setup_max_cpus., and if you are using maxcpus=1,
>> and you have 8 cpus installed, you can put other
>> cpus back online via /sys/interface.
>
> Hmmm.. Strange semantics since maxcpus=0 disables smp completely. No cpu
> can be activated later. Similar to nr_cpus ?

no
for SMP kernel, when nr_cpus=1 is specified, it looks like only one
cpu is installed physically.
smp is still enabled.

maxcpus=0 is really caused misunderstanding.

other maxcpus=1 and other should be rename to boot_online_cpus=


>
>> nr_cpus= is hard limit nr_cpu_ids, so if you have 16 cpus installed,
>> nr_cpus=8 will make your nr_cpu_ids=8, and you can not put back
>> other 8 back. and apic mode could stay with logical flat.
>> this is used to simulate some debug case. for example you have kernel
>> support physflat, and flat, with CONFIG_NR_CPUS=255. to run that on
>> system that only have 8 cpus, you will have apic mode in logical flat.
>>  but if you have run the kernel on system with 32 cpus installed, it
>> will switch to physflat even you have maxcpus=8 appedded.
>
> Ok makes sense.

good.

YH
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/