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Message-Id: <60cbe452-e1f3-4507-9b3b-563906eccb15@app.fastmail.com>
Date: Fri, 30 Aug 2024 17:19:17 -0700
From: "Daniel Xu" <dxu@...uu.xyz>
To: "Alexander Lobakin" <aleksander.lobakin@...el.com>,
"Alexei Starovoitov" <ast@...nel.org>,
"Daniel Borkmann" <daniel@...earbox.net>,
"Andrii Nakryiko" <andrii@...nel.org>
Cc: "Lorenzo Bianconi" <lorenzo@...nel.org>,
"John Fastabend" <john.fastabend@...il.com>,
"Jesper Dangaard Brouer" <hawk@...nel.org>,
"Martin KaFai Lau" <martin.lau@...ux.dev>,
"David Miller" <davem@...emloft.net>, "Eric Dumazet" <edumazet@...gle.com>,
"Jakub Kicinski" <kuba@...nel.org>, "Paolo Abeni" <pabeni@...hat.com>,
"bpf@...r.kernel.org" <bpf@...r.kernel.org>, netdev@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH bpf-next 3/9] net: napi: add ability to create CPU-pinned threaded
NAPI
On Fri, Aug 30, 2024, at 9:25 AM, Alexander Lobakin wrote:
> From: Lorenzo Bianconi <lorenzo@...nel.org>
>
> Add netif_napi_add_percpu() to pin NAPI in threaded mode to a particular
> CPU. This means, if the NAPI is not threaded, it will be run as usually,
> but when switching to threaded mode, it will always be run on the
> specified CPU.
> It's not meant to be used in drivers, but might be useful when creating
> percpu threaded NAPIs, for example, to replace percpu kthreads or
> workers where a NAPI context is needed.
> The already existing netif_napi_add*() are not anyhow affected.
>
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> Signed-off-by: Alexander Lobakin <aleksander.lobakin@...el.com>
> ---
> include/linux/netdevice.h | 35 +++++++++++++++++++++++++++++++++--
> net/core/dev.c | 18 +++++++++++++-----
> 2 files changed, 46 insertions(+), 7 deletions(-)
>
> diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
> index ca5f0dda733b..4d6fb0ccdea1 100644
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -377,6 +377,7 @@ struct napi_struct {
> struct list_head dev_list;
> struct hlist_node napi_hash_node;
> int irq;
> + int thread_cpuid;
> };
>
> enum {
> @@ -2619,8 +2620,18 @@ static inline void netif_napi_set_irq(struct
> napi_struct *napi, int irq)
> */
> #define NAPI_POLL_WEIGHT 64
>
> -void netif_napi_add_weight(struct net_device *dev, struct napi_struct *napi,
> - int (*poll)(struct napi_struct *, int), int weight);
> +void netif_napi_add_weight_percpu(struct net_device *dev,
> + struct napi_struct *napi,
> + int (*poll)(struct napi_struct *, int),
> + int weight, int thread_cpuid);
> +
> +static inline void netif_napi_add_weight(struct net_device *dev,
> + struct napi_struct *napi,
> + int (*poll)(struct napi_struct *, int),
> + int weight)
> +{
> + netif_napi_add_weight_percpu(dev, napi, poll, weight, -1);
> +}
>
> /**
> * netif_napi_add() - initialize a NAPI context
> @@ -2665,6 +2676,26 @@ static inline void netif_napi_add_tx(struct
> net_device *dev,
> netif_napi_add_tx_weight(dev, napi, poll, NAPI_POLL_WEIGHT);
> }
>
> +/**
> + * netif_napi_add_percpu() - initialize a CPU-pinned threaded NAPI
> context
> + * @dev: network device
> + * @napi: NAPI context
> + * @poll: polling function
> + * @thread_cpuid: CPU which this NAPI will be pinned to
> + *
> + * Variant of netif_napi_add() which pins the NAPI to the specified
> CPU. No
> + * changes in the "standard" mode, but in case with the threaded one,
> this
> + * NAPI will always be run on the passed CPU no matter where scheduled.
> + */
> +static inline void netif_napi_add_percpu(struct net_device *dev,
> + struct napi_struct *napi,
> + int (*poll)(struct napi_struct *, int),
> + int thread_cpuid)
> +{
> + netif_napi_add_weight_percpu(dev, napi, poll, NAPI_POLL_WEIGHT,
> + thread_cpuid);
> +}
> +
> /**
> * __netif_napi_del - remove a NAPI context
> * @napi: NAPI context
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 98bb5f890b88..93ca3df8e9dd 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -1428,8 +1428,13 @@ static int napi_kthread_create(struct
> napi_struct *n)
> * TASK_INTERRUPTIBLE mode to avoid the blocked task
> * warning and work with loadavg.
> */
> - n->thread = kthread_run(napi_threaded_poll, n, "napi/%s-%d",
> - n->dev->name, n->napi_id);
> + if (n->thread_cpuid >= 0)
> + n->thread = kthread_run_on_cpu(napi_threaded_poll, n,
> + n->thread_cpuid, "napi/%s-%u",
> + n->dev->name);
> + else
> + n->thread = kthread_run(napi_threaded_poll, n, "napi/%s-%d",
> + n->dev->name, n->napi_id);
> if (IS_ERR(n->thread)) {
> err = PTR_ERR(n->thread);
> pr_err("kthread_run failed with err %d\n", err);
> @@ -6640,8 +6645,10 @@ void netif_queue_set_napi(struct net_device
> *dev, unsigned int queue_index,
> }
> EXPORT_SYMBOL(netif_queue_set_napi);
>
> -void netif_napi_add_weight(struct net_device *dev, struct napi_struct
> *napi,
> - int (*poll)(struct napi_struct *, int), int weight)
> +void netif_napi_add_weight_percpu(struct net_device *dev,
> + struct napi_struct *napi,
> + int (*poll)(struct napi_struct *, int),
> + int weight, int thread_cpuid)
> {
> if (WARN_ON(test_and_set_bit(NAPI_STATE_LISTED, &napi->state)))
> return;
> @@ -6664,6 +6671,7 @@ void netif_napi_add_weight(struct net_device
> *dev, struct napi_struct *napi,
> napi->poll_owner = -1;
> #endif
> napi->list_owner = -1;
> + napi->thread_cpuid = thread_cpuid;
> set_bit(NAPI_STATE_SCHED, &napi->state);
> set_bit(NAPI_STATE_NPSVC, &napi->state);
> list_add_rcu(&napi->dev_list, &dev->napi_list);
> @@ -6677,7 +6685,7 @@ void netif_napi_add_weight(struct net_device
> *dev, struct napi_struct *napi,
> dev->threaded = false;
> netif_napi_set_irq(napi, -1);
> }
> -EXPORT_SYMBOL(netif_napi_add_weight);
> +EXPORT_SYMBOL(netif_napi_add_weight_percpu);
>
> void napi_disable(struct napi_struct *n)
> {
> --
> 2.46.0
Acked-by: Daniel Xu <dxu@...uu.xyz>
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