| Message ID | 20250217-netdevsim-v2-1-fc7fe177b98f@debian.org (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | [net-next,v2] netdevsim: call napi_schedule from a timer context | expand |
On Mon, 17 Feb 2025 09:35:29 -0800 Breno Leitao wrote: > 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. This crashes in the nl_netdev test. I think you should move the hrtimer init to nsim_queue_alloc() and removal to nsim_queue_free()
Hello Jakub, On Mon, Feb 17, 2025 at 11:50:31AM -0800, Jakub Kicinski wrote: > On Mon, 17 Feb 2025 09:35:29 -0800 Breno Leitao wrote: > > 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. > > This crashes in the nl_netdev test. Yea, a nasty crash. Looking at the crash, it seems to be disabling the timer before initializing it, and timer->base was not properly assigned/set. > I think you should move the hrtimer init to nsim_queue_alloc() > and removal to nsim_queue_free() That seems to make nl_netdev happier. Let me do more tests, and then ask NIPA do finish the work. Thanks!
diff --git a/drivers/net/netdevsim/netdev.c b/drivers/net/netdevsim/netdev.c index 9b394ddc5206a7a5ca5440341551aac50c43e20c..57e4ae386e44a9c3f72afc37a3a59d3a504ebad3 100644 --- a/drivers/net/netdevsim/netdev.c +++ b/drivers/net/netdevsim/netdev.c @@ -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; @@ -436,6 +453,7 @@ static void nsim_enable_napi(struct netdevsim *ns) netif_queue_set_napi(dev, i, NETDEV_QUEUE_TYPE_RX, &rq->napi); napi_enable(&rq->napi); + nsim_rq_timer_init(rq); } } @@ -461,6 +479,7 @@ static void nsim_del_napi(struct netdevsim *ns) for (i = 0; i < dev->num_rx_queues; i++) { struct nsim_rq *rq = ns->rq[i]; + hrtimer_cancel(&rq->napi_timer); napi_disable(&rq->napi); __netif_napi_del(&rq->napi); } diff --git a/drivers/net/netdevsim/netdevsim.h b/drivers/net/netdevsim/netdevsim.h index 96d54c08043d3a62b0731efd43bc6a313998bf01..e757f85ed8617bb13ed0bf0e367803e4ddbd8e95 100644 --- a/drivers/net/netdevsim/netdevsim.h +++ b/drivers/net/netdevsim/netdevsim.h @@ -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 {
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: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Breno Leitao <leitao@debian.org> --- Changes in v2: - The approach implemented in v1 will not work, given that ndo_start_xmit() can be called with interrupt disable, and calling local_bh_enable() inside that function has nasty side effected. Jakub suggested creating a timer and calling napi_schedule() from that timer. - Link to v1: https://lore.kernel.org/r/20250212-netdevsim-v1-1-20ece94daae8@debian.org --- drivers/net/netdevsim/netdev.c | 21 ++++++++++++++++++++- drivers/net/netdevsim/netdevsim.h | 1 + 2 files changed, 21 insertions(+), 1 deletion(-) --- base-commit: 0784d83df3bfc977c13252a0599be924f0afa68d change-id: 20250212-netdevsim-258d2d628175 Best regards,