From: Laurent Dufour <ldufour@linux.ibm.com>
To: Thomas Gleixner <tglx@linutronix.de>,
Michael Ellerman <mpe@ellerman.id.au>,
linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org, x86@kernel.org,
dave.hansen@linux.intel.com, mingo@redhat.com, bp@alien8.de,
linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 8/9] powerpc: Add HOTPLUG_SMT support
Date: Mon, 12 Jun 2023 17:20:01 +0200 [thread overview]
Message-ID: <c0fe7b2c-1ce7-3d2f-0175-e61920fc3dee@linux.ibm.com> (raw)
In-Reply-To: <87h6rf81n9.ffs@tglx>
On 10/06/2023 23:10:02, Thomas Gleixner wrote:
> On Thu, Jun 01 2023 at 18:19, Laurent Dufour wrote:
>> @@ -435,12 +435,17 @@ void __init cpu_smt_disable(bool force)
>> * The decision whether SMT is supported can only be done after the full
>> * CPU identification. Called from architecture code.
>> */
>> -void __init cpu_smt_check_topology(unsigned int num_threads)
>> +void __init cpu_smt_check_topology(unsigned int num_threads,
>> + unsigned int max_threads)
>> {
>> if (!topology_smt_supported())
>> cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
>>
>> - cpu_smt_max_threads = num_threads;
>> + cpu_smt_max_threads = max_threads;
>> +
>> + WARN_ON(num_threads > max_threads);
>> + if (num_threads > max_threads)
>> + num_threads = max_threads;
>
> This does not work. The call site does:
>
>> + cpu_smt_check_topology(smt_enabled_at_boot, threads_per_core);
>
> smt_enabled_at_boot is 0 when 'smt-enabled=off', which is not what the
> hotplug core expects. If SMT is disabled it brings up the primary
> thread, which means cpu_smt_num_threads = 1.
Thanks, Thomas,
Definitively, a test against smt_enabled_at_boot==0 is required here.
> This needs more thoughts to avoid a completely inconsistent duct tape
> mess.
Despite the test against smt_enabled_at_boot, mentioned above, I can't see
anything else to rework. Am I missing something?
>
> Btw, the command line parser and the variable smt_enabled_at_boot being
> type int allow negative number of threads too... Maybe not what you want.
I do agree, it should an unsigned type.
Thanks,
Laurent.
> Thanks,
>
> tglx
>
>
>
>
next prev parent reply other threads:[~2023-06-12 17:06 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 15:56 [PATCH 1/9] cpu/SMT: Move SMT prototypes into cpu_smt.h Michael Ellerman
2023-05-24 15:56 ` [PATCH 2/9] cpu/SMT: Move smt/control simple exit cases earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 3/9] cpu/SMT: Store the current/max number of threads Michael Ellerman
2023-06-10 21:26 ` Thomas Gleixner
2023-06-10 22:08 ` Thomas Gleixner
2023-06-13 17:16 ` Laurent Dufour
2023-06-13 18:53 ` Thomas Gleixner
2023-06-14 12:27 ` Laurent Dufour
2023-05-24 15:56 ` [PATCH 4/9] cpu/SMT: Create topology_smt_threads_supported() Michael Ellerman
2023-06-10 22:15 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 5/9] cpu/SMT: Create topology_smt_thread_allowed() Michael Ellerman
2023-06-10 22:35 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs Michael Ellerman
2023-06-10 20:09 ` Thomas Gleixner
2023-06-10 20:13 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 7/9] powerpc/pseries: Initialise CPU hotplug callbacks earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 8/9] powerpc: Add HOTPLUG_SMT support Michael Ellerman
2023-06-01 13:27 ` Laurent Dufour
2023-06-01 16:19 ` Laurent Dufour
2023-06-10 21:10 ` Thomas Gleixner
2023-06-12 15:20 ` Laurent Dufour [this message]
2023-06-12 16:34 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 9/9] powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs Michael Ellerman
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