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Message-ID: <c66e3e800a7d257ef7a90749fe567f056f4c3ace.camel@intel.com>
Date: Sun, 9 Jul 2023 15:25:50 +0000
From: "Zhang, Rui" <rui.zhang@...el.com>
To: "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
"ldufour@...ux.ibm.com" <ldufour@...ux.ibm.com>
CC: "npiggin@...il.com" <npiggin@...il.com>,
"dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
"bp@...en8.de" <bp@...en8.de>,
"mingo@...hat.com" <mingo@...hat.com>,
"tglx@...utronix.de" <tglx@...utronix.de>,
"christophe.leroy@...roup.eu" <christophe.leroy@...roup.eu>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"mpe@...erman.id.au" <mpe@...erman.id.au>,
"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v4 00/10] Introduce SMT level and add PowerPC support
Hi, Laurent,
I ran into a boot hang regression with latest upstream code, and it
took me a while to bisect the offending commit and workaround it.
Now I have tested this patch series on an Intel RaptorLake Hybrid
platform (4 Pcores with HT and 4 Ecores without HT), and it works as
expected.
So, for patch 1~7 in this series,
Tested-by: Zhang Rui <rui.zhang@...el.com>
thanks,
rui
On Wed, 2023-07-05 at 16:51 +0200, Laurent Dufour wrote:
> I'm taking over the series Michael sent previously [1] which is
> smartly
> reviewing the initial series I sent [2]. This series is addressing
> the
> comments sent by Thomas and me on the Michael's one.
>
> Here is a short introduction to the issue this series is addressing:
>
> When a new CPU is added, the kernel is activating all its threads.
> This
> leads to weird, but functional, result when adding CPU on a SMT 4
> system
> for instance.
>
> Here the newly added CPU 1 has 8 threads while the other one has 4
> threads
> active (system has been booted with the 'smt-enabled=4' kernel
> option):
>
> ltcden3-lp12:~ # ppc64_cpu --info
> Core 0: 0* 1* 2* 3* 4 5 6 7
> Core 1: 8* 9* 10* 11* 12* 13* 14* 15*
>
> This mixed SMT level may confused end users and/or some applications.
>
> There is no SMT level recorded in the kernel (common code), neither
> in user
> space, as far as I know. Such a level is helpful when adding new CPU
> or
> when optimizing the energy efficiency (when reactivating CPUs).
>
> When SMP and HOTPLUG_SMT are defined, this series is adding a new SMT
> level
> (cpu_smt_num_threads) and few callbacks allowing the architecture
> code to
> fine control this value, setting a max and a "at boot" level, and
> controling whether a thread should be onlined or not.
>
> v4:
> Rebase on top of 6.5's updates
> Remove a dependancy against the X86's symbol
> cpu_primary_thread_mask
> v3:
> Fix a build error in the patch 6/9
> v2:
> As Thomas suggested,
> Reword some commit's description
> Remove topology_smt_supported()
> Remove topology_smt_threads_supported()
> Introduce CONFIG_SMT_NUM_THREADS_DYNAMIC
> Remove switch() in __store_smt_control()
> Update kernel-parameters.txt
>
> [1]
> https://lore.kernel.org/linuxppc-dev/20230524155630.794584-1-mpe@ellerman.id.au/
> [2]
> https://lore.kernel.org/linuxppc-dev/20230331153905.31698-1-ldufour@linux.ibm.com/
>
>
> Laurent Dufour (2):
> cpu/hotplug: remove dependancy against cpu_primary_thread_mask
> cpu/SMT: Remove topology_smt_supported()
>
> Michael Ellerman (8):
> cpu/SMT: Move SMT prototypes into cpu_smt.h
> cpu/SMT: Move smt/control simple exit cases earlier
> cpu/SMT: Store the current/max number of threads
> cpu/SMT: Create topology_smt_thread_allowed()
> cpu/SMT: Allow enabling partial SMT states via sysfs
> powerpc/pseries: Initialise CPU hotplug callbacks earlier
> powerpc: Add HOTPLUG_SMT support
> powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs
>
> .../ABI/testing/sysfs-devices-system-cpu | 1 +
> .../admin-guide/kernel-parameters.txt | 4 +-
> arch/Kconfig | 3 +
> arch/powerpc/Kconfig | 2 +
> arch/powerpc/include/asm/topology.h | 15 ++
> arch/powerpc/kernel/smp.c | 8 +-
> arch/powerpc/platforms/pseries/hotplug-cpu.c | 30 ++--
> arch/powerpc/platforms/pseries/pseries.h | 2 +
> arch/powerpc/platforms/pseries/setup.c | 2 +
> arch/x86/include/asm/topology.h | 4 +-
> arch/x86/kernel/cpu/common.c | 2 +-
> arch/x86/kernel/smpboot.c | 8 -
> include/linux/cpu.h | 25 +--
> include/linux/cpu_smt.h | 33 ++++
> kernel/cpu.c | 142 +++++++++++++---
> --
> 15 files changed, 196 insertions(+), 85 deletions(-)
> create mode 100644 include/linux/cpu_smt.h
>
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