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From: James Morse <james.morse@arm.com>
To: Brice Goglin <Brice.Goglin@inria.fr>
Cc: Jeremy Linton <Jeremy.Linton@arm.com>,
	linux-arm-kernel@lists.infradead.org
Subject: Re: offline CPUs shown in sysfs core_siblings mask
Date: Wed, 11 Sep 2019 17:06:24 +0100	[thread overview]
Message-ID: <4568af7d-724e-5ee7-3ba1-87a5db662447@arm.com> (raw)
In-Reply-To: <c1596783-cd14-8247-3c42-faa052c5c066@inria.fr>

Hi Brice,

(CC: +Jeremy)

On 9/11/19 2:23 PM, Brice Goglin wrote:
> We have a report from a user of hwloc/lstopo on ThunderX2 that complains
> that offline CPUs are shown in sysfs cpu core_siblings files.

Hmmm, this doesn't happen on my TX2, running mainline:
root@eglon:/sys/devices/system/cpu# cat cpu1/topology/core_siblings
00000000,00000000,00000000,00000000,ffffffff,ffffffff,ffffffff,ffffffff
root@eglon:/sys/devices/system/cpu# echo 0 > cpu0/online
root@eglon:/sys/devices/system/cpu# cat cpu1/topology/core_siblings
00000000,00000000,00000000,00000000,ffffffff,ffffffff,ffffffff,fffffffe
root@eglon:/sys/devices/system/cpu# echo 1 > cpu0/online
root@eglon:/sys/devices/system/cpu# cat cpu1/topology/core_siblings
00000000,00000000,00000000,00000000,ffffffff,ffffffff,ffffffff,ffffffff


> Only 8 online logicial CPUs, but 56 are shown in these masks. This is on
> RHEL7 with a kernel 4.14.0-115.2.2.el7a.aarch64 but I couldn't find any
> significant change in Linux git.

Could you try a recent mainline kernel?

Does your system have an ACPI PPTT table? (I assume its ACPI)

Prior to the ACPI PPTT table handling, it wasn't possible for an arm64 
ACPI system to know about packages and threads.


> I guess thread_siblings has the same behavior but I couldn't test it.

(this would depend on the firmware table too)


Thanks,

James

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  reply	other threads:[~2019-09-11 16:06 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-11 13:23 offline CPUs shown in sysfs core_siblings mask Brice Goglin
2019-09-11 16:06 ` James Morse [this message]
2019-09-11 16:14   ` Sudeep Holla
2019-09-12  8:09   ` Brice Goglin

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