From: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
Cc: linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 2/2] powerpc/numa: Return the first online node if device tree mapping returns a not online node
Date: Fri, 24 Jun 2022 14:20:47 +0530 [thread overview]
Message-ID: <20220624085047.GB145013@linux.vnet.ibm.com> (raw)
In-Reply-To: <20220623125442.645240-2-aneesh.kumar@linux.ibm.com>
* Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com> [2022-06-23 18:24:42]:
> While building the cpu_to_node map make sure we always use the online node
> to build the mapping table. In general this should not be an issue
> because the kernel use similar lookup mechanism (vphn_get_nid()) to mark
> nodes online (setup_node_data()). Hence NUMA nodes we find during
> lookup in numa_setup_cpu() will always be found online.
>
> To keep logic simpler/correct, make sure that if the hypervisor
> or device tree returned a not online node, don't use that to build
> the map table. Instead, use the first_online_node.
Why should the returned nid be already online. Are we facing any problem
with the current code?
Since general idea is to keep cpu_to_node constant, By assigining it the
first_online_node, we may be ending up assigning a wrong node, resulting a
performance penalty later on. i.e CPU may actually belong to node 4 but we
assigned it to node 1. Also the coregroup id is derived from associavity
array. If there is a mismatch between the coregroup id and nid,
scheduler will crib.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
> arch/powerpc/mm/numa.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/mm/numa.c b/arch/powerpc/mm/numa.c
> index 0801b2ce9b7d..f387b9eb9dc9 100644
> --- a/arch/powerpc/mm/numa.c
> +++ b/arch/powerpc/mm/numa.c
> @@ -741,7 +741,7 @@ static int numa_setup_cpu(unsigned long lcpu)
> of_node_put(cpu);
>
> out_present:
> - if (nid < 0 || !node_possible(nid))
> + if (nid < 0 || !node_online(nid))
> nid = first_online_node;
>
> /*
> --
> 2.36.1
>
--
Thanks and Regards
Srikar Dronamraju
next prev parent reply other threads:[~2022-06-24 8:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-06-23 12:54 [PATCH 1/2] powerpc/numa: Return the first online node instead of 0 Aneesh Kumar K.V
2022-06-23 12:54 ` [PATCH 2/2] powerpc/numa: Return the first online node if device tree mapping returns a not online node Aneesh Kumar K.V
2022-06-24 8:50 ` Srikar Dronamraju [this message]
2022-06-27 5:27 ` Aneesh Kumar K.V
2022-06-24 8:39 ` [PATCH 1/2] powerpc/numa: Return the first online node instead of 0 Srikar Dronamraju
2022-06-27 14:05 ` Aneesh Kumar K.V
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