From:   Thomas Gleixner <tglx@linutronix.de>
To:     Sourabh Jain <sourabhjain@linux.ibm.com>,
        Eric DeVolder <eric.devolder@oracle.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org,
        kexec@lists.infradead.org, ebiederm@xmission.com,
        dyoung@redhat.com, bhe@redhat.com, vgoyal@redhat.com
Cc:     mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com,
        hpa@zytor.com, nramas@linux.microsoft.com, thomas.lendacky@amd.com,
        robh@kernel.org, efault@gmx.de, rppt@kernel.org, david@redhat.com,
        konrad.wilk@oracle.com, boris.ostrovsky@oracle.com
Subject: Re: [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr
 notes
In-Reply-To: <f7c0269b-05e7-c706-f111-c768d4a13b72@linux.ibm.com>
References: <20230131224236.122805-1-eric.devolder@oracle.com>
 <20230131224236.122805-6-eric.devolder@oracle.com> <87sffpzkle.ffs@tglx>
 <dd03f47a-0017-6239-04e9-e796dca03c0c@oracle.com> <87h6vw2rwf.ffs@tglx>
 <7580421a-648a-2c4b-3c33-82e7622d9585@oracle.com>
 <d465173e-a31a-c4d6-af51-59d9ff0c2edc@linux.ibm.com>
 <24034f33-739b-e5f5-40c0-8d5abeb1ad89@oracle.com>
 <18c57fd0-2ad0-361a-9a53-ac49c372f021@linux.ibm.com>
 <b3d5c730-60ee-8f1c-978c-e3df41e3a3f1@oracle.com>
 <f7c0269b-05e7-c706-f111-c768d4a13b72@linux.ibm.com>
Date:   Mon, 13 Feb 2023 13:52:50 +0100
Message-ID: <87ttzpzpzx.ffs@tglx>
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On Mon, Feb 13 2023 at 10:10, Sourabh Jain wrote:
> The sysconf document says _SC_NPROCESSORS_CONF is processors configured, 
> isn't that equivalent to possible CPUs?

glibc tries to evaluate that in the following order:

  1) /sys/devices/system/cpu/cpu*

     That's present CPUs not possible CPUs

  2) /proc/stat

     That's online CPUs

  3) sched_getaffinity()

     That's online CPUs at best. In the worst case it's an affinity mask
     which is set on a process group

Thanks,

        tglx