From mboxrd@z Thu Jan  1 00:00:00 1970
From: Joerg Vehlow <lkml@jv-coder.de>
Date: Mon, 30 Nov 2020 09:30:54 +0100
Subject: [LTP] [PATCH v3] overcommit_memory: Fix unstable subtest
In-Reply-To: <87360rnuio.fsf@suse.de>
References: <20201127071419.20370-1-lkml@jv-coder.de> <87360rnuio.fsf@suse.de>
Message-ID: <01818271-8dba-96a3-76f3-575243c93243@jv-coder.de>
List-Id: <ltp.lists.linux.it>
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
To: ltp@lists.linux.it

Hi,
>> +static long get_total_batch_size_bytes(void)
>> +{
>> +	struct sysinfo info;
>> +	long ncpus = tst_ncpus_conf();
> I'm not completely sure if this is the same value as num_cpus_present()
> in the kernel? I'm just wondering if CPU hotplugging could result in the
> wrong value being calculated (other than if it is hotplugged while the test
> is running).

I was thinking about this as well when I implemented this. Here is my 
reasoning:

If hotplug is disabled possible=present and possible=nr cpus at boot. 
Otherwise present is the real number of existing (not necessarily 
enabled cpus), and possible=NR_CPU
In both cases it is the number of cpus installed in the system, enabled 
or not.

tst_ncpus_conf is _SC_NPROCESSORS_CONF, which is documented as "returns 
the number of processors the operating system configured. But it might 
be possible for the operating system to disable individual processors 
and so the call", in contrast to _SC_NPROCESSORS_ONLN "returns the 
number of processors which are currently online (i.e., available).".

I would interpret _SC_NPROCESSORS_CONF as equal to present and 
_SC_NPROCESSORS_ONLN as equal to online.

Anything flaw in my logic?

J?rg