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kernel: add support for threaded network backlog processing

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This can improve load balancing by pushing backlog (and RPS) processing
to separate threads, allowing the scheduler to distribute the load.
It can be enabled with: echo 1 > /proc/sys/net/core/backlog_threaded

Signed-off-by: Felix Fietkau <nbd@nbd.name>
This commit is contained in:
Felix Fietkau 2023-02-19 15:01:43 +01:00
parent 47de2c6862
commit 4ce0405e18
2 changed files with 229 additions and 5 deletions
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10
target/linux/generic/hack-5.15/721-net-add-packet-mangeling.patch
View File

@ -19,7 +19,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -1676,6 +1676,10 @@ enum netdev_priv_flags {
@@ -1677,6 +1677,10 @@ enum netdev_priv_flags {
IFF_TX_SKB_NO_LINEAR = BIT_ULL(31),
};
@ -30,7 +30,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
#define IFF_802_1Q_VLAN IFF_802_1Q_VLAN
#define IFF_EBRIDGE IFF_EBRIDGE
#define IFF_BONDING IFF_BONDING
@@ -1708,6 +1712,7 @@ enum netdev_priv_flags {
@@ -1709,6 +1713,7 @@ enum netdev_priv_flags {
#define IFF_L3MDEV_RX_HANDLER IFF_L3MDEV_RX_HANDLER
#define IFF_LIVE_RENAME_OK IFF_LIVE_RENAME_OK
#define IFF_TX_SKB_NO_LINEAR IFF_TX_SKB_NO_LINEAR
@ -38,7 +38,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
/* Specifies the type of the struct net_device::ml_priv pointer */
enum netdev_ml_priv_type {
@@ -2009,6 +2014,7 @@ struct net_device {
@@ -2010,6 +2015,7 @@ struct net_device {
/* Read-mostly cache-line for fast-path access */
unsigned int flags;
unsigned int priv_flags;
@ -46,7 +46,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
const struct net_device_ops *netdev_ops;
int ifindex;
unsigned short gflags;
@@ -2069,6 +2075,11 @@ struct net_device {
@@ -2070,6 +2076,11 @@ struct net_device {
const struct tlsdev_ops *tlsdev_ops;
#endif
@ -58,7 +58,7 @@ Signed-off-by: Felix Fietkau <nbd@nbd.name>
const struct header_ops *header_ops;
unsigned char operstate;
@@ -2143,6 +2154,10 @@ struct net_device {
@@ -2144,6 +2155,10 @@ struct net_device {
struct mctp_dev __rcu *mctp_ptr;
#endif

224
target/linux/generic/pending-5.15/760-net-core-add-optional-threading-for-backlog-processi.patch Normal file
View File

@ -0,0 +1,224 @@
From: Felix Fietkau <nbd@nbd.name>
Date: Thu, 16 Feb 2023 18:39:04 +0100
Subject: [PATCH] net/core: add optional threading for backlog processing
When dealing with few flows or an imbalance on CPU utilization, static RPS
CPU assignment can be too inflexible. Add support for enabling threaded NAPI
for backlog processing in order to allow the scheduler to better balance
processing. This helps better spread the load across idle CPUs.
Signed-off-by: Felix Fietkau <nbd@nbd.name>
---
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -500,6 +500,7 @@ static inline bool napi_complete(struct
}
int dev_set_threaded(struct net_device *dev, bool threaded);
+int backlog_set_threaded(bool threaded);
/**
* napi_disable - prevent NAPI from scheduling
@@ -3363,6 +3364,7 @@ struct softnet_data {
unsigned int processed;
unsigned int time_squeeze;
unsigned int received_rps;
+ unsigned int process_queue_empty;
#ifdef CONFIG_RPS
struct softnet_data *rps_ipi_list;
#endif
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4574,7 +4574,7 @@ static int rps_ipi_queued(struct softnet
#ifdef CONFIG_RPS
struct softnet_data *mysd = this_cpu_ptr(&softnet_data);
- if (sd != mysd) {
+ if (sd != mysd && !test_bit(NAPI_STATE_THREADED, &sd->backlog.state)) {
sd->rps_ipi_next = mysd->rps_ipi_list;
mysd->rps_ipi_list = sd;
@@ -5755,6 +5755,8 @@ static DEFINE_PER_CPU(struct work_struct
/* Network device is going away, flush any packets still pending */
static void flush_backlog(struct work_struct *work)
{
+ unsigned int process_queue_empty;
+ bool threaded, flush_processq;
struct sk_buff *skb, *tmp;
struct softnet_data *sd;
@@ -5770,9 +5772,18 @@ static void flush_backlog(struct work_st
input_queue_head_incr(sd);
}
}
+
+ threaded = test_bit(NAPI_STATE_THREADED, &sd->backlog.state);
+ flush_processq = threaded &&
+ !skb_queue_empty_lockless(&sd->process_queue);
+ if (flush_processq)
+ process_queue_empty = sd->process_queue_empty;
rps_unlock(sd);
local_irq_enable();
+ if (threaded)
+ goto out;
+
skb_queue_walk_safe(&sd->process_queue, skb, tmp) {
if (skb->dev->reg_state == NETREG_UNREGISTERING) {
__skb_unlink(skb, &sd->process_queue);
@@ -5780,7 +5791,18 @@ static void flush_backlog(struct work_st
input_queue_head_incr(sd);
}
}
+
+out:
local_bh_enable();
+
+ while (flush_processq) {
+ msleep(1);
+ local_irq_disable();
+ rps_lock(sd);
+ flush_processq = process_queue_empty == sd->process_queue_empty;
+ rps_unlock(sd);
+ local_irq_enable();
+ }
}
static bool flush_required(int cpu)
@@ -6463,6 +6485,7 @@ static int process_backlog(struct napi_s
local_irq_disable();
rps_lock(sd);
+ sd->process_queue_empty++;
if (skb_queue_empty(&sd->input_pkt_queue)) {
/*
* Inline a custom version of __napi_complete().
@@ -6472,7 +6495,8 @@ static int process_backlog(struct napi_s
* We can use a plain write instead of clear_bit(),
* and we dont need an smp_mb() memory barrier.
*/
- napi->state = 0;
+ napi->state &= ~(NAPIF_STATE_SCHED |
+ NAPIF_STATE_SCHED_THREADED);
again = false;
} else {
skb_queue_splice_tail_init(&sd->input_pkt_queue,
@@ -6889,6 +6913,57 @@ int dev_set_threaded(struct net_device *
}
EXPORT_SYMBOL(dev_set_threaded);
+int backlog_set_threaded(bool threaded)
+{
+ static bool backlog_threaded;
+ int err = 0;
+ int i;
+
+ if (backlog_threaded == threaded)
+ return 0;
+
+ for_each_possible_cpu(i) {
+ struct softnet_data *sd = &per_cpu(softnet_data, i);
+ struct napi_struct *n = &sd->backlog;
+
+ if (n->thread)
+ continue;
+ n->thread = kthread_run(napi_threaded_poll, n, "napi/backlog-%d", i);
+ if (IS_ERR(n->thread)) {
+ err = PTR_ERR(n->thread);
+ pr_err("kthread_run failed with err %d\n", err);
+ n->thread = NULL;
+ threaded = false;
+ break;
+ }
+
+ }
+
+ backlog_threaded = threaded;
+
+ /* Make sure kthread is created before THREADED bit
+ * is set.
+ */
+ smp_mb__before_atomic();
+
+ for_each_possible_cpu(i) {
+ struct softnet_data *sd = &per_cpu(softnet_data, i);
+ struct napi_struct *n = &sd->backlog;
+ unsigned long flags;
+
+ local_irq_save(flags);
+ rps_lock(sd);
+ if (threaded)
+ n->state |= NAPIF_STATE_THREADED;
+ else
+ n->state &= ~NAPIF_STATE_THREADED;
+ rps_unlock(sd);
+ local_irq_restore(flags);
+ }
+
+ return err;
+}
+
void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
int (*poll)(struct napi_struct *, int), int weight)
{
@@ -11367,6 +11442,9 @@ static int dev_cpu_dead(unsigned int old
raise_softirq_irqoff(NET_TX_SOFTIRQ);
local_irq_enable();
+ if (test_bit(NAPI_STATE_THREADED, &oldsd->backlog.state))
+ return 0;
+
#ifdef CONFIG_RPS
remsd = oldsd->rps_ipi_list;
oldsd->rps_ipi_list = NULL;
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -28,6 +28,7 @@ static int int_3600 = 3600;
static int min_sndbuf = SOCK_MIN_SNDBUF;
static int min_rcvbuf = SOCK_MIN_RCVBUF;
static int max_skb_frags = MAX_SKB_FRAGS;
+static int backlog_threaded;
static long long_one __maybe_unused = 1;
static long long_max __maybe_unused = LONG_MAX;
@@ -114,6 +115,23 @@ static int rps_sock_flow_sysctl(struct c
}
#endif /* CONFIG_RPS */
+static int backlog_threaded_sysctl(struct ctl_table *table, int write,
+ void *buffer, size_t *lenp, loff_t *ppos)
+{
+ static DEFINE_MUTEX(backlog_threaded_mutex);
+ int ret;
+
+ mutex_lock(&backlog_threaded_mutex);
+
+ ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
+ if (write && !ret)
+ ret = backlog_set_threaded(backlog_threaded);
+
+ mutex_unlock(&backlog_threaded_mutex);
+
+ return ret;
+}
+
#ifdef CONFIG_NET_FLOW_LIMIT
static DEFINE_MUTEX(flow_limit_update_mutex);
@@ -470,6 +488,15 @@ static struct ctl_table net_core_table[]
.proc_handler = rps_sock_flow_sysctl
},
#endif
+ {
+ .procname = "backlog_threaded",
+ .data = &backlog_threaded,
+ .maxlen = sizeof(unsigned int),
+ .mode = 0644,
+ .proc_handler = backlog_threaded_sysctl,
+ .extra1 = SYSCTL_ZERO,
+ .extra2 = SYSCTL_ONE
+ },
#ifdef CONFIG_NET_FLOW_LIMIT
{
.procname = "flow_limit_cpu_bitmap",