Hi Felix,
On Sat, 25 Jul 2020 19:57:23 +0200 Felix Fietkau wrote:
> On 2020-07-25 10:16, Hillf Danton wrote:
> > Hi folks
> >
> > Below is a minimunm poc implementation I can imagine on top of workqueue
> > to make napi threaded. Thoughts are appreciated.
> >
> Hi Hillf,
>
> For some reason I don't see your mails on linux-wireless/netdev.
All is down to my inbox ...
> I've cleaned up your implementation a bit and I ran some tests with mt76
> on an mt7621 embedded board. The results look pretty nice, performance
> is a lot more consistent in my tests now.
Thanks very much for your cleanup and testing.
> Here are the changes that I've made compared to your version:
>
> - remove the #ifdef, I think it's unnecessary
This makes the code a mile nicer and perhaps I fear pulls some questions
from EricD.
> - add a state bit for threaded NAPI
> - make netif_threaded_napi_add inline
> - run queue_work outside of local_irq_save/restore (it does that
> internally already)
>
> If you don't mind, I'd like to propose this to netdev soon. Can I have
> your Signed-off-by for that?
Feel free to do that. Is it likely for me to select a Cc?
Thanks
Hillf
> Thanks,
>
> - Felix
>
> ---
> --- a/include/linux/netdevice.h
> +++ b/include/linux/netdevice.h
> @@ -347,6 +347,7 @@ struct napi_struct {
> struct list_head dev_list;
> struct hlist_node napi_hash_node;
> unsigned int napi_id;
> + struct work_struct work;
> };
>
> enum {
> @@ -357,6 +358,7 @@ enum {
> NAPI_STATE_HASHED, /* In NAPI hash (busy polling possible) */
> NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
> NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
> + NAPI_STATE_THREADED, /* Use threaded NAPI */
> };
>
> enum {
> @@ -367,6 +369,7 @@ enum {
> NAPIF_STATE_HASHED = BIT(NAPI_STATE_HASHED),
> NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
> NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
> + NAPIF_STATE_THREADED = BIT(NAPI_STATE_THREADED),
> };
>
> enum gro_result {
> @@ -2315,6 +2318,26 @@ static inline void *netdev_priv(const struct
> net_device *dev)
> void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
> int (*poll)(struct napi_struct *, int), int weight);
>
> +/**
> + * netif_threaded_napi_add - initialize a NAPI context
> + * @dev: network device
> + * @napi: NAPI context
> + * @poll: polling function
> + * @weight: default weight
> + *
> + * This variant of netif_napi_add() should be used from drivers using NAPI
> + * with CPU intensive poll functions.
> + * This will schedule polling from a high priority workqueue that
> + */
> +static inline void netif_threaded_napi_add(struct net_device *dev,
> + struct napi_struct *napi,
> + int (*poll)(struct napi_struct *,
> int),
> + int weight)
> +{
> + set_bit(NAPI_STATE_THREADED, &napi->state);
> + netif_napi_add(dev, napi, poll, weight);
> +}
> +
> /**
> * netif_tx_napi_add - initialize a NAPI context
> * @dev: network device
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -158,6 +158,7 @@ static DEFINE_SPINLOCK(offload_lock);
> struct list_head ptype_base[PTYPE_HASH_SIZE] __read_mostly;
> struct list_head ptype_all __read_mostly; /* Taps */
> static struct list_head offload_base __read_mostly;
> +static struct workqueue_struct *napi_workq;
Is __read_mostly missing?
> static int netif_rx_internal(struct sk_buff *skb);
> static int call_netdevice_notifiers_info(unsigned long val,
> @@ -6286,6 +6287,11 @@ void __napi_schedule(struct napi_struct *n)
> {
> unsigned long flags;
>
> + if (test_bit(NAPI_STATE_THREADED, &n->state)) {
> + queue_work(napi_workq, &n->work);
> + return;
> + }
> +
> local_irq_save(flags);
> ____napi_schedule(this_cpu_ptr(&softnet_data), n);
> local_irq_restore(flags);
> @@ -6333,6 +6339,11 @@ EXPORT_SYMBOL(napi_schedule_prep);
> */
> void __napi_schedule_irqoff(struct napi_struct *n)
> {
> + if (test_bit(NAPI_STATE_THREADED, &n->state)) {
> + queue_work(napi_workq, &n->work);
> + return;
> + }
> +
> ____napi_schedule(this_cpu_ptr(&softnet_data), n);
> }
> EXPORT_SYMBOL(__napi_schedule_irqoff);
> @@ -6601,6 +6612,29 @@ static void init_gro_hash(struct napi_struct *napi)
> napi->gro_bitmask = 0;
> }
>
> +static void napi_workfn(struct work_struct *work)
> +{
> + struct napi_struct *n = container_of(work, struct napi_struct, work);
> +
> + for (;;) {
> + if (!test_bit(NAPI_STATE_SCHED, &n->state))
> + return;
> +
> + if (n->poll(n, n->weight) < n->weight)
> + return;
> +
> + if (need_resched()) {
> + /*
> + * have to pay for the latency of task switch even if
> + * napi is scheduled
> + */
> + if (test_bit(NAPI_STATE_SCHED, &n->state))
> + queue_work(napi_workq, work);
> + return;
> + }
> + }
> +}
> +
> void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
> int (*poll)(struct napi_struct *, int), int weight)
> {
> @@ -6621,6 +6655,7 @@ void netif_napi_add(struct net_device *dev, struct
> napi_struct *napi,
> #ifdef CONFIG_NETPOLL
> napi->poll_owner = -1;
> #endif
> + INIT_WORK(&napi->work, napi_workfn);
> set_bit(NAPI_STATE_SCHED, &napi->state);
> napi_hash_add(napi);
> }
> @@ -10676,6 +10711,10 @@ static int __init net_dev_init(void)
> sd->backlog.weight = weight_p;
> }
>
> + napi_workq = alloc_workqueue("napi_workq", WQ_UNBOUND | WQ_HIGHPRI,
> + WQ_UNBOUND_MAX_ACTIVE);
> + BUG_ON(!napi_workq);
> +
> dev_boot_phase = 0;
>
> /* The loopback device is special if any other network devices
>
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