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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
Date: Mon, 13 Feb 2023 13:52:50 +0100	[thread overview]
Message-ID: <87ttzpzpzx.ffs@tglx> (raw)
In-Reply-To: <f7c0269b-05e7-c706-f111-c768d4a13b72@linux.ibm.com>

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

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WARNING: multiple messages have this Message-ID (diff)
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
Date: Mon, 13 Feb 2023 13:52:50 +0100	[thread overview]
Message-ID: <87ttzpzpzx.ffs@tglx> (raw)
In-Reply-To: <f7c0269b-05e7-c706-f111-c768d4a13b72@linux.ibm.com>

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

  reply	other threads:[~2023-02-13 12:53 UTC|newest]

Thread overview: 70+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-01-31 22:42 [PATCH v18 0/7] crash: Kernel handling of CPU and memory hot un/plug Eric DeVolder
2023-01-31 22:42 ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 1/7] crash: move a few code bits to setup support of crash hotplug Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 2/7] crash: prototype change for crash_prepare_elf64_headers() Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 3/7] crash: add generic infrastructure for crash hotplug support Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-02-09 19:10   ` Sourabh Jain
2023-02-09 19:10     ` Sourabh Jain
2023-02-10 16:51     ` Eric DeVolder
2023-02-10 16:51       ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 4/7] kexec: exclude elfcorehdr from the segment digest Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 5/7] kexec: exclude hot remove cpu from elfcorehdr notes Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-02-01 11:33   ` Thomas Gleixner
2023-02-01 11:33     ` Thomas Gleixner
2023-02-06  8:12     ` Sourabh Jain
2023-02-06  8:12       ` Sourabh Jain
2023-02-06 13:03       ` Thomas Gleixner
2023-02-06 13:03         ` Thomas Gleixner
2023-02-07 17:23     ` Eric DeVolder
2023-02-07 17:23       ` Eric DeVolder
2023-02-08 13:44       ` Thomas Gleixner
2023-02-08 13:44         ` Thomas Gleixner
2023-02-09 17:31         ` Eric DeVolder
2023-02-09 17:31           ` Eric DeVolder
2023-02-09 18:43           ` Sourabh Jain
2023-02-09 18:43             ` Sourabh Jain
2023-02-09 19:39             ` Eric DeVolder
2023-02-09 19:39               ` Eric DeVolder
2023-02-10  6:29               ` Sourabh Jain
2023-02-10  6:29                 ` Sourabh Jain
2023-02-11  0:35                 ` Eric DeVolder
2023-02-11  0:35                   ` Eric DeVolder
2023-02-13  4:40                   ` Sourabh Jain
2023-02-13  4:40                     ` Sourabh Jain
2023-02-13 12:52                     ` Thomas Gleixner [this message]
2023-02-13 12:52                       ` Thomas Gleixner
2023-02-15  2:53                       ` Sourabh Jain
2023-02-15  2:53                         ` Sourabh Jain
2023-02-28 12:44                     ` Baoquan He
2023-02-28 12:44                       ` Baoquan He
2023-02-28 18:52                       ` Eric DeVolder
2023-02-28 18:52                         ` Eric DeVolder
2023-03-01 15:48                         ` Eric DeVolder
2023-03-01 15:48                           ` Eric DeVolder
2023-03-02 10:51                           ` Baoquan He
2023-03-02 10:51                             ` Baoquan He
2023-03-02  5:23                         ` Sourabh Jain
2023-03-02  5:23                           ` Sourabh Jain
2023-02-23 20:34                 ` Eric DeVolder
2023-02-23 20:34                   ` Eric DeVolder
2023-02-24  8:34                   ` Sourabh Jain
2023-02-24  8:34                     ` Sourabh Jain
2023-02-24 20:16                     ` Eric DeVolder
2023-02-24 20:16                       ` Eric DeVolder
2023-02-27  6:11                       ` Sourabh Jain
2023-02-27  6:11                         ` Sourabh Jain
2023-02-28 21:50                         ` Eric DeVolder
2023-02-28 21:50                           ` Eric DeVolder
2023-03-01  6:22                           ` Sourabh Jain
2023-03-01  6:22                             ` Sourabh Jain
2023-03-01 14:16                             ` Eric DeVolder
2023-03-01 14:16                               ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 6/7] crash: memory and cpu hotplug sysfs attributes Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder
2023-01-31 22:42 ` [PATCH v18 7/7] x86/crash: add x86 crash hotplug support Eric DeVolder
2023-01-31 22:42   ` Eric DeVolder

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