linux-kernel - Re: [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes

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Message-ID: <87ttzpzpzx.ffs@tglx>
Date:   Mon, 13 Feb 2023 13:52:50 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Sourabh Jain <sourabhjain@...ux.ibm.com>,
        Eric DeVolder <eric.devolder@...cle.com>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        kexec@...ts.infradead.org, ebiederm@...ssion.com,
        dyoung@...hat.com, bhe@...hat.com, vgoyal@...hat.com
Cc:     mingo@...hat.com, bp@...en8.de, dave.hansen@...ux.intel.com,
        hpa@...or.com, nramas@...ux.microsoft.com, thomas.lendacky@....com,
        robh@...nel.org, efault@....de, rppt@...nel.org, david@...hat.com,
        konrad.wilk@...cle.com, boris.ostrovsky@...cle.com
Subject: Re: [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr
 notes

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