Commit bf3624cf authored by Breno Leitao's avatar Breno Leitao Committed by Jakub Kicinski
Browse files

netdevsim: call napi_schedule from a timer context 



The netdevsim driver was experiencing NOHZ tick-stop errors during packet
transmission due to pending softirq work when calling napi_schedule().
This issue was observed when running the netconsole selftest, which
triggered the following error message:

  NOHZ tick-stop error: local softirq work is pending, handler #08!!!

To fix this issue, introduce a timer that schedules napi_schedule()
from a timer context instead of calling it directly from the TX path.

Create an hrtimer for each queue and kick it from the TX path,
which then schedules napi_schedule() from the timer context.

Suggested-by: default avatarJakub Kicinski <kuba@kernel.org>
Signed-off-by: default avatarBreno Leitao <leitao@debian.org>
Link: https://patch.msgid.link/20250219-netdevsim-v3-1-811e2b8abc4c@debian.org


Signed-off-by: default avatarJakub Kicinski <kuba@kernel.org>
parent 372ab5a5

drivers/net/netdevsim/netdev.c

+20 −1
Original line number Diff line number Diff line
@@ -87,7 +87,8 @@ static netdev_tx_t nsim_start_xmit(struct sk_buff *skb, struct net_device *dev) 
	if (unlikely(nsim_forward_skb(peer_dev, skb, rq) == NET_RX_DROP))

		goto out_drop_cnt;



	napi_schedule(&rq->napi);

	if (!hrtimer_active(&rq->napi_timer))

		hrtimer_start(&rq->napi_timer, us_to_ktime(5), HRTIMER_MODE_REL);



	rcu_read_unlock();

	u64_stats_update_begin(&ns->syncp);
@@ -426,6 +427,22 @@ static int nsim_init_napi(struct netdevsim *ns) 
	return err;

}



static enum hrtimer_restart nsim_napi_schedule(struct hrtimer *timer)

{

	struct nsim_rq *rq;



	rq = container_of(timer, struct nsim_rq, napi_timer);

	napi_schedule(&rq->napi);



	return HRTIMER_NORESTART;

}



static void nsim_rq_timer_init(struct nsim_rq *rq)

{

	hrtimer_init(&rq->napi_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);

	rq->napi_timer.function = nsim_napi_schedule;

}



static void nsim_enable_napi(struct netdevsim *ns)

{

	struct net_device *dev = ns->netdev;
@@ -615,11 +632,13 @@ static struct nsim_rq *nsim_queue_alloc(void) 
		return NULL;



	skb_queue_head_init(&rq->skb_queue);

	nsim_rq_timer_init(rq);

	return rq;

}



static void nsim_queue_free(struct nsim_rq *rq)

{

	hrtimer_cancel(&rq->napi_timer);

	skb_queue_purge_reason(&rq->skb_queue, SKB_DROP_REASON_QUEUE_PURGE);

	kfree(rq);

}

drivers/net/netdevsim/netdevsim.h

+1 −0
Original line number Diff line number Diff line
@@ -97,6 +97,7 @@ struct nsim_rq { 
	struct napi_struct napi;

	struct sk_buff_head skb_queue;

	struct page_pool *page_pool;

	struct hrtimer napi_timer;

};



struct netdevsim {