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From: Thomas Gleixner <tglx@linutronix.de>
To: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.ibm.com>,
	Laurent Dufour <ldufour@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	Nicholas Piggin <npiggin@gmail.com>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Michal Suchanek <msuchanek@suse.de>,
	linuxppc-dev@lists.ozlabs.org,
	"Nysal Jan K.A." <nysal@linux.ibm.com>
Subject: Re: [PATCH 0/2] Skip offline cores when enabling SMT on PowerPC
Date: Mon, 24 Jun 2024 23:24:11 +0200	[thread overview]
Message-ID: <87sex26nlw.ffs@tglx> (raw)
In-Reply-To: <11f9cc04-91eb-4a70-9ff0-5c6f24483cd3@linux.ibm.com>

On Tue, Jun 25 2024 at 00:41, Shrikanth Hegde wrote:
> On 6/24/24 1:44 AM, Thomas Gleixner wrote:
>> Right. So changing it not to online a thread when the full core is
>> offline should not really break stuff.
>> 
>> OTH, the mechanism to figure that out on x86 is definitely different and
>> more complicated than on power because the sibling threads are not
>> having consecutive CPU numbers.
>
> wouldn't topology_sibling_cpumask have this info? 
> If the mask is empty does it mean the core is offline? 

The mask is not yet available for the to be brought up CPU. That's
established when the CPU boots. It might work because all threads are
brought up during early boot for !~*&^!@% reasons, but then it won't
work under all circumstances, e.g. 'maxcpus=$N'.

We could fix that now with the new topology enumeration code, but that's
a larger scale project.

Thanks,

        tglx

WARNING: multiple messages have this Message-ID (diff)
From: Thomas Gleixner <tglx@linutronix.de>
To: Shrikanth Hegde <sshegde@linux.ibm.com>
Cc: Tyrel Datwyler <tyreld@linux.ibm.com>,
	Michal Suchanek <msuchanek@suse.de>,
	Nicholas Piggin <npiggin@gmail.com>,
	Christophe Leroy <christophe.leroy@csgroup.eu>,
	"Naveen N. Rao" <naveen.n.rao@linux.ibm.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Laurent Dufour <ldufour@linux.ibm.com>,
	linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org,
	Michael Ellerman <mpe@ellerman.id.au>,
	"Nysal Jan K.A." <nysal@linux.ibm.com>
Subject: Re: [PATCH 0/2] Skip offline cores when enabling SMT on PowerPC
Date: Mon, 24 Jun 2024 23:24:11 +0200	[thread overview]
Message-ID: <87sex26nlw.ffs@tglx> (raw)
In-Reply-To: <11f9cc04-91eb-4a70-9ff0-5c6f24483cd3@linux.ibm.com>

On Tue, Jun 25 2024 at 00:41, Shrikanth Hegde wrote:
> On 6/24/24 1:44 AM, Thomas Gleixner wrote:
>> Right. So changing it not to online a thread when the full core is
>> offline should not really break stuff.
>> 
>> OTH, the mechanism to figure that out on x86 is definitely different and
>> more complicated than on power because the sibling threads are not
>> having consecutive CPU numbers.
>
> wouldn't topology_sibling_cpumask have this info? 
> If the mask is empty does it mean the core is offline? 

The mask is not yet available for the to be brought up CPU. That's
established when the CPU boots. It might work because all threads are
brought up during early boot for !~*&^!@% reasons, but then it won't
work under all circumstances, e.g. 'maxcpus=$N'.

We could fix that now with the new topology enumeration code, but that's
a larger scale project.

Thanks,

        tglx

  reply	other threads:[~2024-06-24 21:25 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-06-12 18:50 [PATCH 0/2] Skip offline cores when enabling SMT on PowerPC Nysal Jan K.A.
2024-06-12 18:50 ` Nysal Jan K.A.
2024-06-12 18:50 ` [PATCH 1/2] cpu/SMT: Enable SMT only if a core is online Nysal Jan K.A.
2024-06-12 18:50   ` Nysal Jan K.A.
2024-06-12 18:50 ` [PATCH 2/2] powerpc/topology: Check " Nysal Jan K.A.
2024-06-12 18:50   ` Nysal Jan K.A.
2024-06-24 19:06   ` Shrikanth Hegde
2024-06-24 19:06     ` Shrikanth Hegde
2024-06-25  6:13     ` Nysal Jan K.A.
2024-06-25  6:13       ` Nysal Jan K.A.
2024-06-13 11:34 ` [PATCH 0/2] Skip offline cores when enabling SMT on PowerPC Michael Ellerman
2024-06-13 11:34   ` Michael Ellerman
2024-06-13 12:07   ` Michal Suchánek
2024-06-13 12:07     ` Michal Suchánek
2024-06-14  3:52   ` Nysal Jan K.A.
2024-06-14  3:52     ` Nysal Jan K.A.
2024-06-23 20:14   ` Thomas Gleixner
2024-06-23 20:14     ` Thomas Gleixner
2024-06-24 19:11     ` Shrikanth Hegde
2024-06-24 19:11       ` Shrikanth Hegde
2024-06-24 21:24       ` Thomas Gleixner [this message]
2024-06-24 21:24         ` Thomas Gleixner
2024-07-01  4:54         ` Shrikanth Hegde
2024-07-01  4:54           ` Shrikanth Hegde

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