linux-kernel - Re: [PATCH v8 1/2] nvme-multipath: prepare for "queue-depth" iopolicy

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Message-ID: <0130bbae-8e63-42a1-b579-f122c55566d4@nvidia.com>
Date: Wed, 26 Jun 2024 08:02:52 +0000
From: Chaitanya Kulkarni <chaitanyak@...dia.com>
To: John Meneghini <jmeneghi@...hat.com>, "kbusch@...nel.org"
	<kbusch@...nel.org>, "hch@....de" <hch@....de>, "sagi@...mberg.me"
	<sagi@...mberg.me>
CC: "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"emilne@...hat.com" <emilne@...hat.com>, "jrani@...estorage.com"
	<jrani@...estorage.com>, "randyj@...estorage.com" <randyj@...estorage.com>,
	"hare@...nel.org" <hare@...nel.org>
Subject: Re: [PATCH v8 1/2] nvme-multipath: prepare for "queue-depth" iopolicy

On 6/25/24 05:26, John Meneghini wrote:
> This patch prepares for the introduction of a new iopolicy by breaking up
> the nvme_find_path() code path into sub-routines.
>
> Signed-off-by: John Meneghini <jmeneghi@...hat.com>
> ---
>   drivers/nvme/host/multipath.c | 21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/nvme/host/multipath.c b/drivers/nvme/host/multipath.c
> index 8a4d0e377114..0ade378e514b 100644
> --- a/drivers/nvme/host/multipath.c
> +++ b/drivers/nvme/host/multipath.c
> @@ -291,10 +291,14 @@ static struct nvme_ns *nvme_next_ns(struct nvme_ns_head *head,
>   	return list_first_or_null_rcu(&head->list, struct nvme_ns, siblings);
>   }
>   
> -static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head,
> -		int node, struct nvme_ns *old)
> +static struct nvme_ns *nvme_round_robin_path(struct nvme_ns_head *head)
>   {
>   	struct nvme_ns *ns, *found = NULL;
> +	int node = numa_node_id();
> +	struct nvme_ns *old = srcu_dereference(head->current_path[node], &head->srcu);
> +
> +	if (unlikely(!old))
> +		return __nvme_find_path(head, node);

nit:- above looks little bit odd with long line, I'd just :-

         struct nvme_ns *old;

         old = srcu_dereference(head->current_path[node], &head->srcu);
         if (unlikely(!old))
                 return __nvme_find_path(head, node);


>   
>   	if (list_is_singular(&head->list)) {
>   		if (nvme_path_is_disabled(old))
> @@ -340,7 +344,7 @@ static inline bool nvme_path_is_optimized(struct nvme_ns *ns)
>   		ns->ana_state == NVME_ANA_OPTIMIZED;
>   }
>   
> -inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
> +static struct nvme_ns *nvme_numa_path(struct nvme_ns_head *head)
>   {
>   	int node = numa_node_id();
>   	struct nvme_ns *ns;
> @@ -348,14 +352,19 @@ inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
>   	ns = srcu_dereference(head->current_path[node], &head->srcu);
>   	if (unlikely(!ns))
>   		return __nvme_find_path(head, node);
> -
> -	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
> -		return nvme_round_robin_path(head, node, ns);
>   	if (unlikely(!nvme_path_is_optimized(ns)))
>   		return __nvme_find_path(head, node);
>   	return ns;
>   }
>   
> +inline struct nvme_ns *nvme_find_path(struct nvme_ns_head *head)
> +{
> +	if (READ_ONCE(head->subsys->iopolicy) == NVME_IOPOLICY_RR)
> +		return nvme_round_robin_path(head);
> +	else
> +		return nvme_numa_path(head);

nit: - else is not needed ...

Looks good.

Reviewed-by: Chaitanya Kulkarni <kch@...dia.com>

-ck