linux-kernel - Re: [PATCH v2] arch_topology: Make cluster topology span at least SMT CPUs

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Date:   Sat, 3 Sep 2022 08:00:55 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Yicong Yang <yangyicong@...wei.com>
Cc:     sudeep.holla@....com, vincent.guittot@...aro.org,
        ionela.voinescu@....com, linux-kernel@...r.kernel.org,
        rafael@...nel.org, 21cnbao@...il.com, jonathan.cameron@...wei.com,
        linuxarm@...wei.com, prime.zeng@...wei.com,
        yangyicong@...ilicon.com
Subject: Re: [PATCH v2] arch_topology: Make cluster topology span at least
 SMT CPUs

On Thu, Aug 25, 2022 at 05:20:07PM +0800, Yicong Yang wrote:
> From: Yicong Yang <yangyicong@...ilicon.com>
> 
> Currently cpu_clustergroup_mask() will return CPU mask if cluster span more
> or the same CPUs as cpu_coregroup_mask(). This will result topology borken
> on non-Cluster SMT machines when building with CONFIG_SCHED_CLUSTER=y.
> 
> Test with:
> qemu-system-aarch64 -enable-kvm -machine virt \
>  -net none \
>  -cpu host \
>  -bios ./QEMU_EFI.fd \
>  -m 2G \
>  -smp 48,sockets=2,cores=12,threads=2 \
>  -kernel $Image \
>  -initrd $Rootfs \
>  -nographic \
>  -append "rdinit=init console=ttyAMA0 sched_verbose loglevel=8"
> 
> We'll get below error:
> [    3.084568] BUG: arch topology borken
> [    3.084570]      the SMT domain not a subset of the CLS domain
> 
> Since cluster is a level higher than SMT, fix this by making cluster
> spans at least SMT CPUs.
> 
> Cc: Sudeep Holla <sudeep.holla@....com>
> Cc: Vincent Guittot <vincent.guittot@...aro.org>
> Cc: Ionela Voinescu <ionela.voinescu@....com>
> Fixes: bfcc4397435d ("arch_topology: Limit span of cpu_clustergroup_mask()")
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>
> Reviewed-by: Ionela Voinescu <ionela.voinescu@....com>
> ---
> Change since v1:
> - mention the kernel config CONFIG_SCHED_CLUSTER=y, per Ionela
> Link:https://lore.kernel.org/lkml/20220823073044.58697-1-yangyicong@huawei.com/
> 
>  drivers/base/arch_topology.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 0424b59b695e..0056a1273275 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -724,7 +724,7 @@ const struct cpumask *cpu_clustergroup_mask(int cpu)
>  	 */
>  	if (cpumask_subset(cpu_coregroup_mask(cpu),
>  			   &cpu_topology[cpu].cluster_sibling))
> -		return get_cpu_mask(cpu);
> +		return cpu_smt_mask(cpu);

As the kernel-test robot reported, this breaks the build on some
architectures, so I'll go and revert it from my tree now.

thanks,

greg k-h