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From 47ef17d783884e8073f09f0d6ecbe94f2a3d9d12 Mon Sep 17 00:00:00 2001
From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Mon, 15 Aug 2022 17:29:50 +0200
Subject: [PATCH 09/68] net: Avoid the IPI to free the
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/6.1/older/patches-6.1.141-rt52.tar.xz
skb_attempt_defer_free() collects a skbs, which was allocated on a
remote CPU, on a per-CPU list. These skbs are either freed on that
remote CPU once the CPU enters NET_RX or an remote IPI function is
invoked in to raise the NET_RX softirq if a threshold of pending skb has
been exceeded.
This remote IPI can cause the wakeup of ksoftirqd on PREEMPT_RT if the
remote CPU idle was idle. This is undesired because once the ksoftirqd
is running it will acquire all pending softirqs and they will not be
executed as part of the threaded interrupt until ksoftird goes idle
again.
To void all this, schedule the deferred clean up from a worker.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
include/linux/netdevice.h | 4 ++++
net/core/dev.c | 37 ++++++++++++++++++++++++++++---------
net/core/skbuff.c | 7 ++++++-
3 files changed, 38 insertions(+), 10 deletions(-)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index f44701b82ea8..4a2d2995054e 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -3199,7 +3199,11 @@ struct softnet_data {
int defer_count;
int defer_ipi_scheduled;
struct sk_buff *defer_list;
+#ifndef CONFIG_PREEMPT_RT
call_single_data_t defer_csd;
+#else
+ struct work_struct defer_work;
+#endif
};
static inline void input_queue_head_incr(struct softnet_data *sd)
diff --git a/net/core/dev.c b/net/core/dev.c
index 8e57eae40221..eeba2e1890ac 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4662,15 +4662,6 @@ static void rps_trigger_softirq(void *data)
#endif /* CONFIG_RPS */
-/* Called from hardirq (IPI) context */
-static void trigger_rx_softirq(void *data)
-{
- struct softnet_data *sd = data;
-
- __raise_softirq_irqoff(NET_RX_SOFTIRQ);
- smp_store_release(&sd->defer_ipi_scheduled, 0);
-}
-
/*
* Check if this softnet_data structure is another cpu one
* If yes, queue it to our IPI list and return 1
@@ -6731,6 +6722,30 @@ static void skb_defer_free_flush(struct softnet_data *sd)
}
}
+#ifndef CONFIG_PREEMPT_RT
+/* Called from hardirq (IPI) context */
+static void trigger_rx_softirq(void *data)
+{
+ struct softnet_data *sd = data;
+
+ __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+ smp_store_release(&sd->defer_ipi_scheduled, 0);
+}
+
+#else
+
+static void trigger_rx_softirq(struct work_struct *defer_work)
+{
+ struct softnet_data *sd;
+
+ sd = container_of(defer_work, struct softnet_data, defer_work);
+ smp_store_release(&sd->defer_ipi_scheduled, 0);
+ local_bh_disable();
+ skb_defer_free_flush(sd);
+ local_bh_enable();
+}
+#endif
+
static __latent_entropy void net_rx_action(struct softirq_action *h)
{
struct softnet_data *sd = this_cpu_ptr(&softnet_data);
@@ -11547,7 +11562,11 @@ static int __init net_dev_init(void)
INIT_CSD(&sd->csd, rps_trigger_softirq, sd);
sd->cpu = i;
#endif
+#ifndef CONFIG_PREEMPT_RT
INIT_CSD(&sd->defer_csd, trigger_rx_softirq, sd);
+#else
+ INIT_WORK(&sd->defer_work, trigger_rx_softirq);
+#endif
spin_lock_init(&sd->defer_lock);
init_gro_hash(&sd->backlog);
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index d8a3ada886ff..df66874683b7 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -6696,6 +6696,11 @@ nodefer: __kfree_skb(skb);
/* Make sure to trigger NET_RX_SOFTIRQ on the remote CPU
* if we are unlucky enough (this seems very unlikely).
*/
- if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1))
+ if (unlikely(kick) && !cmpxchg(&sd->defer_ipi_scheduled, 0, 1)) {
+#ifndef CONFIG_PREEMPT_RT
smp_call_function_single_async(cpu, &sd->defer_csd);
+#else
+ schedule_work_on(cpu, &sd->defer_work);
+#endif
+ }
}
--
2.49.0
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