0004-Added-sysctl-option-to-enable-threaded-napi-at-runti.patch

From 093e59d29c0c4f0554745f1f68e95437d4ddcecb Mon Sep 17 00:00:00 2001
From: Riccardo Mancini <r.mancini@santannapisa.it>
Date: Sun, 23 Jun 2019 22:18:03 +0200
Subject: [PATCH 4/4] Added sysctl option to enable threaded napi at runtime

A delay is needed since switching too fast creates bugs in the approach
I used. The proper way would have been using some sort of syncronization
mechanism but in this case it is not trivial. In the way the threaded
NAPI is written, bugs can only occour if the value is switched too fast,
within a napi poll. This limitation won't hurt users since I don't think
anyone would want to change it that fast.
---
 include/linux/netdevice.h  |  4 ++++
 kernel/sysctl_binary.c     |  3 +++
 net/core/dev.c             | 29 ++++++++++++++++++++++++++-
 net/core/sysctl_net_core.c | 41 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 76 insertions(+), 1 deletion(-)

diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index eeacebd7debb..3da3875a0093 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -368,6 +368,10 @@ enum gro_result {
 };
 typedef enum gro_result gro_result_t;
 
+#ifdef CONFIG_THREADED_NAPI
+extern int knapid_enabled;
+#endif
+
 /*
  * enum rx_handler_result - Possible return values for rx_handlers.
  * @RX_HANDLER_CONSUMED: skb was consumed by rx_handler, do not process it
diff --git a/kernel/sysctl_binary.c b/kernel/sysctl_binary.c
index 73c132095a7b..813e6c3ee2b0 100644
--- a/kernel/sysctl_binary.c
+++ b/kernel/sysctl_binary.c
@@ -196,6 +196,9 @@ static const struct bin_table bin_net_core_table[] = {
 	{ CTL_INT,	NET_CORE_DEV_WEIGHT,	"dev_weight" },
 	{ CTL_INT,	NET_CORE_SOMAXCONN,	"somaxconn" },
 	{ CTL_INT,	NET_CORE_BUDGET,	"netdev_budget" },
+	#ifdef CONFIG_THREADED_NAPI
+	{ CTL_INT,	NET_CORE_KNAPID,	"knapid_enabled" },
+	#endif
 	{ CTL_INT,	NET_CORE_AEVENT_ETIME,	"xfrm_aevent_etime" },
 	{ CTL_INT,	NET_CORE_AEVENT_RSEQTH,	"xfrm_aevent_rseqth" },
 	{ CTL_INT,	NET_CORE_WARNINGS,	"warnings" },
diff --git a/net/core/dev.c b/net/core/dev.c
index 7629651f3485..fceccdf77719 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6429,19 +6429,38 @@ static __latent_entropy int napi_poll_everything(void)
 	int budget = netdev_budget;
     	int ret = 0;
 
+#ifdef CONFIG_THREADED_NAPI
+	int was_napi_running;
+#endif
+
 	LIST_HEAD(list);
 	LIST_HEAD(repoll);
 
 	local_irq_disable();
 	list_splice_init(&sd->poll_list, &list);
+
+#ifdef CONFIG_THREADED_NAPI
+	was_napi_running = __this_cpu_read(napi_running);
+	 __this_cpu_write(napi_running, 1);
+#endif
+
 	local_irq_enable();
 
+#ifdef CONFIG_THREADED_NAPI
+	if (was_napi_running)
+		return 0;
+#endif
+
 	for (;;) {
 		struct napi_struct *n;
 
 		if (list_empty(&list)) {
-			if (!sd_has_rps_ipi_waiting(sd) && list_empty(&repoll))
+			if (!sd_has_rps_ipi_waiting(sd) && list_empty(&repoll)){
+#ifdef CONFIG_THREADED_NAPI
+				this_cpu_write(napi_running, 0);
+#endif
 				goto out;
+			}
 			break;
 		}
 
@@ -6467,6 +6486,10 @@ static __latent_entropy int napi_poll_everything(void)
 	if (!list_empty(&sd->poll_list))
 		ret = 1;
 
+#ifdef CONFIG_THREADED_NAPI
+	__this_cpu_write(napi_running, 0);
+#endif
+
 	net_rps_action_and_irq_enable(sd);
 out:
 	__kfree_skb_flush();
@@ -6481,6 +6504,9 @@ static void net_rx_action(struct softirq_action *h)
 		// I still have work to do
 		if (!knapid_enabled)
 			raise_softirq(NET_RX_SOFTIRQ);
+		else{
+			wakeup_napid();
+		}
 	}
 }
 
@@ -6501,6 +6527,7 @@ static int knapid_should_run(unsigned int cpu)
 	if (ret){
 		// I still have work to do
 		if (!knapid_enabled){
+			raise_softirq(NET_RX_SOFTIRQ);
 			return 0;
 		} else
 			return 1;
diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 1a2685694abd..8c25ae019c9f 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -313,6 +313,36 @@ proc_dolongvec_minmax_bpf_restricted(struct ctl_table *table, int write,
 }
 #endif
 
+#ifdef CONFIG_THREADED_NAPI
+unsigned long next_allowed_knapid_enable = 0;
+static int KNAPID_ENABLE_INTERVAL = 10000000;
+DEFINE_MUTEX(knapid_enable_mutex);
+
+static int proc_dointvec_minmax_knapid_enable(struct ctl_table *table, int write,
+					   void __user *buffer, size_t *lenp,
+					   loff_t *ppos)
+{
+	int ret, old_val;
+
+	mutex_lock(&knapid_enable_mutex);
+
+	old_val = knapid_enabled;
+
+	if (write && time_before(jiffies, next_allowed_knapid_enable)){
+		ret = -EPERM;
+		goto out;
+ 	}
+
+	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+
+	if (knapid_enabled != old_val)
+		next_allowed_knapid_enable = jiffies + usecs_to_jiffies(KNAPID_ENABLE_INTERVAL);
+out:
+	mutex_unlock(&knapid_enable_mutex);
+	return ret;
+}
+#endif
+
 static struct ctl_table net_core_table[] = {
 #ifdef CONFIG_NET
 	{
@@ -562,6 +592,17 @@ static struct ctl_table net_core_table[] = {
 		.extra1		= &zero,
 		.extra2		= &two,
 	},
+#ifdef CONFIG_THREADED_NAPI
+	{
+		.procname	= "knapid_enable",
+		.data		= &knapid_enabled,
+		.maxlen		= sizeof(int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax_knapid_enable,
+		.extra1		= &zero,
+		.extra2		= &one,		
+	},
+#endif
 	{ }
 };
 
-- 
2.21.0