linux-kernel - Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts with lower layer

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Date:   Tue, 31 Dec 2019 16:40:51 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     z00214469 <prime.zeng@...ilicon.com>
Cc:     linuxarm@...wei.com,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-kernel@...r.kernel.org, Sudeep Holla <sudeep.holla@....com>,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH] cpu-topology: warn if NUMA configurations conflicts with
 lower layer

On Mon, Dec 23, 2019 at 04:16:19PM +0800, z00214469 wrote:
> As we know, from sched domain's perspective, the DIE layer should be
> larger than or at least equal to the MC layer, and in some cases, MC
> is defined by the arch specified hardware, MPIDR for example, but NUMA
> can be defined by users,

Who are the users you are referring above ?

> with the following system configrations:

Do you mean ACPI tables or DT or some firmware tables ?

> *************************************
> NUMA:      	 0-2,  3-7

Is the above simply wrong with respect to hardware and it actually match
core_siblings ?

> core_siblings:   0-3,  4-7
> *************************************
> Per the current code, for core 3, its MC cpu map fallbacks to 3~7(its
> core_sibings is 0~3 while its numa node map is 3~7).
>
> For the sched MC, when we are build sched groups:
> step1. core3 's sched groups chain is built like this: 3->4->5->6->7->3
> step2. core4's sched groups chain is built like this: 4->5->6->7->4
> so after step2, core3's sched groups for MC level is overlapped, more
> importantly, it will fall to dead loop if while(sg != sg->groups)
>
> Obviously, the NUMA node with cpu 3-7 conflict with the MC level cpu
> map, but unfortunately, there is no way even detect such cases.
>

Again, is cpu 3-7 actually in a NUMA node or is it 4-7 ?

> In this patch, prompt a warning message to help with the above cases.
>
> Signed-off-by: Zeng Tao <prime.zeng@...ilicon.com>
> ---
>  drivers/base/arch_topology.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/base/arch_topology.c b/drivers/base/arch_topology.c
> index 1eb81f11..5fe44b3 100644
> --- a/drivers/base/arch_topology.c
> +++ b/drivers/base/arch_topology.c
> @@ -439,10 +439,18 @@ const struct cpumask *cpu_coregroup_mask(int cpu)
>  	if (cpumask_subset(&cpu_topology[cpu].core_sibling, core_mask)) {
>  		/* not numa in package, lets use the package siblings */
>  		core_mask = &cpu_topology[cpu].core_sibling;
> -	}
> +	} else
> +		pr_warn_once("Warning: suspicous broken topology: cpu:[%d]'s core_sibling:[%*pbl] not a subset of numa node:[%*pbl]\n",
> +			cpu, cpumask_pr_args(&cpu_topology[cpu].core_sibling),
> +			cpumask_pr_args(core_mask));
> +

Won't this print warning on all systems that don't have numa within a
package ? What are you trying to achieve here ?

>  	if (cpu_topology[cpu].llc_id != -1) {
>  		if (cpumask_subset(&cpu_topology[cpu].llc_sibling, core_mask))
>  			core_mask = &cpu_topology[cpu].llc_sibling;
> +		else
> +			pr_warn_once("Warning: suspicous broken topology: cpu:[%d]'s llc_sibling:[%*pbl] not a subset of numa node:[%*pbl]\n",
> +				cpu, cpumask_pr_args(&cpu_topology[cpu].llc_sibling),
> +				cpumask_pr_args(core_mask));
>  	}
>

This will trigger warning on all systems that lack cacheinfo topology.
I don't understand the intent of this patch at all. Can you explain
all the steps you follow and the issue you face ?

--
Regards,
Sudeep