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From: Sudeep Holla <sudeep.holla@arm.com>
To: James Morse <james.morse@arm.com>
Cc: Sudeep Holla <sudeep.holla@arm.com>,
	linux-arm-kernel@lists.infradead.org,
	Jeremy Linton <Jeremy.Linton@arm.com>,
	Brice Goglin <Brice.Goglin@inria.fr>
Subject: Re: offline CPUs shown in sysfs core_siblings mask
Date: Wed, 11 Sep 2019 17:14:41 +0100	[thread overview]
Message-ID: <20190911161441.GB5433@e107533-lin.cambridge.arm.com> (raw)
In-Reply-To: <4568af7d-724e-5ee7-3ba1-87a5db662447@arm.com>

On Wed, Sep 11, 2019 at 05:06:24PM +0100, James Morse wrote:
> 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
> 

Commit 7f9545aa1a91 ("arm64: smp: remove cpu and numa topology information when hotplugging out CPU")
is the patch that introduced that changes to update the sibling masks when
CPUs are hotplugged out. Before that patch the behaviour was same as you
describe. AFAIK, they were not marked stable and never backported.

> 
> > 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.
>

Indeed yes, but not sure if that fixes the above mentioned issue.

> 
> > I guess thread_siblings has the same behavior but I couldn't test it.
> 
> (this would depend on the firmware table too)
>

If the above commit doesn't fix it, then it's a bug. I didn't test them on
SMT systems for sure.

--
Regards,
Sudeep

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  reply	other threads:[~2019-09-11 16:15 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
2019-09-11 16:14   ` Sudeep Holla [this message]
2019-09-12  8:09   ` Brice Goglin

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