From: Björn Töpel <bjorn.topel@xxxxxxxxx>
The existing busy-polling mode, enabled by the SO_BUSY_POLL socket
option or system-wide using the /proc/sys/net/core/busy_read knob, is
an opportunistic. That means that if the NAPI context is not
scheduled, it will poll it. If, after busy-polling, the budget is
exceeded the busy-polling logic will schedule the NAPI onto the
regular softirq handling.
One implication of the behavior above is that a busy/heavy loaded NAPI
context will never enter/allow for busy-polling. Some applications
prefer that most NAPI processing would be done by busy-polling.
This series adds a new socket option, SO_PREFER_BUSY_POLL, that works
in concert with the napi_defer_hard_irqs and gro_flush_timeout
knobs. The napi_defer_hard_irqs and gro_flush_timeout knobs were
introduced in commit 6f8b12d661d0 ("net: napi: add hard irqs deferral
feature"), and allows for a user to defer interrupts to be enabled and
instead schedule the NAPI context from a watchdog timer. When a user
enables the SO_PREFER_BUSY_POLL, again with the other knobs enabled,
and the NAPI context is being processed by a softirq, the softirq NAPI
processing will exit early to allow the busy-polling to be performed.
If the application stops performing busy-polling via a system call,
the watchdog timer defined by gro_flush_timeout will timeout, and
regular softirq handling will resume.
In summary; Heavy traffic applications that prefer busy-polling over
softirq processing should use this option.
Example usage:
$ echo 2 | sudo tee /sys/class/net/ens785f1/napi_defer_hard_irqs
$ echo 200000 | sudo tee /sys/class/net/ens785f1/gro_flush_timeout
Note that the timeout should be larger than the userspace processing
window, otherwise the watchdog will timeout and fall back to regular
softirq processing.
Enable the SO_BUSY_POLL/SO_PREFER_BUSY_POLL options on your socket.
Signed-off-by: Björn Töpel <bjorn.topel@xxxxxxxxx>
---
arch/alpha/include/uapi/asm/socket.h | 2 +
arch/mips/include/uapi/asm/socket.h | 2 +
arch/parisc/include/uapi/asm/socket.h | 2 +
arch/sparc/include/uapi/asm/socket.h | 2 +
fs/eventpoll.c | 2 +-
include/linux/netdevice.h | 35 +++++++-----
include/net/busy_poll.h | 5 +-
include/net/sock.h | 4 ++
include/uapi/asm-generic/socket.h | 2 +
net/core/dev.c | 78 +++++++++++++++++++++------
net/core/sock.c | 9 ++++
11 files changed, 111 insertions(+), 32 deletions(-)
diff --git a/arch/alpha/include/uapi/asm/socket.h b/arch/alpha/include/uapi/asm/socket.h
index de6c4df61082..538359642554 100644
--- a/arch/alpha/include/uapi/asm/socket.h
+++ b/arch/alpha/include/uapi/asm/socket.h
@@ -124,6 +124,8 @@
#define SO_DETACH_REUSEPORT_BPF 68
+#define SO_PREFER_BUSY_POLL 69
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/mips/include/uapi/asm/socket.h b/arch/mips/include/uapi/asm/socket.h
index d0a9ed2ca2d6..e406e73b5e6e 100644
--- a/arch/mips/include/uapi/asm/socket.h
+++ b/arch/mips/include/uapi/asm/socket.h
@@ -135,6 +135,8 @@
#define SO_DETACH_REUSEPORT_BPF 68
+#define SO_PREFER_BUSY_POLL 69
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/parisc/include/uapi/asm/socket.h b/arch/parisc/include/uapi/asm/socket.h
index 10173c32195e..1bc46200889d 100644
--- a/arch/parisc/include/uapi/asm/socket.h
+++ b/arch/parisc/include/uapi/asm/socket.h
@@ -116,6 +116,8 @@
#define SO_DETACH_REUSEPORT_BPF 0x4042
+#define SO_PREFER_BUSY_POLL 0x4043
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64
diff --git a/arch/sparc/include/uapi/asm/socket.h b/arch/sparc/include/uapi/asm/socket.h
index 8029b681fc7c..99688cf673a4 100644
--- a/arch/sparc/include/uapi/asm/socket.h
+++ b/arch/sparc/include/uapi/asm/socket.h
@@ -117,6 +117,8 @@
#define SO_DETACH_REUSEPORT_BPF 0x0047
+#define SO_PREFER_BUSY_POLL 0x0048
+
#if !defined(__KERNEL__)
diff --git a/fs/eventpoll.c b/fs/eventpoll.c
index 4df61129566d..e11fab3a0b9e 100644
--- a/fs/eventpoll.c
+++ b/fs/eventpoll.c
@@ -397,7 +397,7 @@ static void ep_busy_loop(struct eventpoll *ep, int nonblock)
unsigned int napi_id = READ_ONCE(ep->napi_id);
if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on())
- napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep);
+ napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep, false);
}
static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep)
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index 7ce648a564f7..52d1cc2bd8a7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -350,23 +350,25 @@ struct napi_struct {
};
enum {
- NAPI_STATE_SCHED, /* Poll is scheduled */
- NAPI_STATE_MISSED, /* reschedule a napi */
- NAPI_STATE_DISABLE, /* Disable pending */
- NAPI_STATE_NPSVC, /* Netpoll - don't dequeue from poll_list */
- NAPI_STATE_LISTED, /* NAPI added to system lists */
- NAPI_STATE_NO_BUSY_POLL,/* Do not add in napi_hash, no busy polling */
- NAPI_STATE_IN_BUSY_POLL,/* sk_busy_loop() owns this NAPI */
+ NAPI_STATE_SCHED, /* Poll is scheduled */
+ NAPI_STATE_MISSED, /* reschedule a napi */
+ NAPI_STATE_DISABLE, /* Disable pending */
+ NAPI_STATE_NPSVC, /* Netpoll - don't dequeue from poll_list */
+ NAPI_STATE_LISTED, /* NAPI added to system lists */
+ NAPI_STATE_NO_BUSY_POLL, /* Do not add in napi_hash, no busy polling */
+ NAPI_STATE_IN_BUSY_POLL, /* sk_busy_loop() owns this NAPI */
+ NAPI_STATE_PREFER_BUSY_POLL, /* prefer busy-polling over softirq processing*/
};
enum {
- NAPIF_STATE_SCHED = BIT(NAPI_STATE_SCHED),
- NAPIF_STATE_MISSED = BIT(NAPI_STATE_MISSED),
- NAPIF_STATE_DISABLE = BIT(NAPI_STATE_DISABLE),
- NAPIF_STATE_NPSVC = BIT(NAPI_STATE_NPSVC),
- NAPIF_STATE_LISTED = BIT(NAPI_STATE_LISTED),
- NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
- NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
+ NAPIF_STATE_SCHED = BIT(NAPI_STATE_SCHED),
+ NAPIF_STATE_MISSED = BIT(NAPI_STATE_MISSED),
+ NAPIF_STATE_DISABLE = BIT(NAPI_STATE_DISABLE),
+ NAPIF_STATE_NPSVC = BIT(NAPI_STATE_NPSVC),
+ NAPIF_STATE_LISTED = BIT(NAPI_STATE_LISTED),
+ NAPIF_STATE_NO_BUSY_POLL = BIT(NAPI_STATE_NO_BUSY_POLL),
+ NAPIF_STATE_IN_BUSY_POLL = BIT(NAPI_STATE_IN_BUSY_POLL),
+ NAPIF_STATE_PREFER_BUSY_POLL = BIT(NAPI_STATE_PREFER_BUSY_POLL),
};
enum gro_result {
@@ -437,6 +439,11 @@ static inline bool napi_disable_pending(struct napi_struct *n)
return test_bit(NAPI_STATE_DISABLE, &n->state);
}
+static inline bool napi_prefer_busy_poll(struct napi_struct *n)
+{
+ return test_bit(NAPI_STATE_PREFER_BUSY_POLL, &n->state);
+}
+
bool napi_schedule_prep(struct napi_struct *n);
/**
diff --git a/include/net/busy_poll.h b/include/net/busy_poll.h
index b001fa91c14e..0292b8353d7e 100644
--- a/include/net/busy_poll.h
+++ b/include/net/busy_poll.h
@@ -43,7 +43,7 @@ bool sk_busy_loop_end(void *p, unsigned long start_time);
void napi_busy_loop(unsigned int napi_id,
bool (*loop_end)(void *, unsigned long),
- void *loop_end_arg);
+ void *loop_end_arg, bool prefer_busy_poll);
#else /* CONFIG_NET_RX_BUSY_POLL */
static inline unsigned long net_busy_loop_on(void)
@@ -105,7 +105,8 @@ static inline void sk_busy_loop(struct sock *sk, int nonblock)
unsigned int napi_id = READ_ONCE(sk->sk_napi_id);
if (napi_id >= MIN_NAPI_ID)
- napi_busy_loop(napi_id, nonblock ? NULL : sk_busy_loop_end, sk);
+ napi_busy_loop(napi_id, nonblock ? NULL : sk_busy_loop_end, sk,
+ READ_ONCE(sk->sk_prefer_busy_poll));
#endif
}
diff --git a/include/net/sock.h b/include/net/sock.h
index a5c6ae78df77..d49b89b071b6 100644
--- a/include/net/sock.h
+++ b/include/net/sock.h
@@ -301,6 +301,7 @@ struct bpf_local_storage;
* @sk_ack_backlog: current listen backlog
* @sk_max_ack_backlog: listen backlog set in listen()
* @sk_uid: user id of owner
+ * @sk_prefer_busy_poll: prefer busypolling over softirq processing
* @sk_priority: %SO_PRIORITY setting
* @sk_type: socket type (%SOCK_STREAM, etc)
* @sk_protocol: which protocol this socket belongs in this network family
@@ -479,6 +480,9 @@ struct sock {
u32 sk_ack_backlog;
u32 sk_max_ack_backlog;
kuid_t sk_uid;
+#ifdef CONFIG_NET_RX_BUSY_POLL
+ u8 sk_prefer_busy_poll;
+#endif
struct pid *sk_peer_pid;
const struct cred *sk_peer_cred;
long sk_rcvtimeo;
diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h
index 77f7c1638eb1..7dd02408b7ce 100644
--- a/include/uapi/asm-generic/socket.h
+++ b/include/uapi/asm-generic/socket.h
@@ -119,6 +119,8 @@
#define SO_DETACH_REUSEPORT_BPF 68
+#define SO_PREFER_BUSY_POLL 69
+
#if !defined(__KERNEL__)
#if __BITS_PER_LONG == 64 || (defined(__x86_64__) && defined(__ILP32__))
diff --git a/net/core/dev.c b/net/core/dev.c
index 60d325bda0d7..6f8d2cffb7c5 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6458,7 +6458,8 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
WARN_ON_ONCE(!(val & NAPIF_STATE_SCHED));
- new = val & ~(NAPIF_STATE_MISSED | NAPIF_STATE_SCHED);
+ new = val & ~(NAPIF_STATE_MISSED | NAPIF_STATE_SCHED |
+ NAPIF_STATE_PREFER_BUSY_POLL);
/* If STATE_MISSED was set, leave STATE_SCHED set,
* because we will call napi->poll() one more time.
@@ -6497,8 +6498,29 @@ static struct napi_struct *napi_by_id(unsigned int napi_id)
#define BUSY_POLL_BUDGET 8
-static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock)
+static void __busy_poll_stop(struct napi_struct *napi, bool skip_schedule)
{
+ if (!skip_schedule) {
+ gro_normal_list(napi);
+ __napi_schedule(napi);
+ return;
+ }
+
+ if (napi->gro_bitmask) {
+ /* flush too old packets
+ * If HZ < 1000, flush all packets.
+ */
+ napi_gro_flush(napi, HZ >= 1000);
+ }
+
+ gro_normal_list(napi);
+ clear_bit(NAPI_STATE_SCHED, &napi->state);
+}
+
+static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock, bool prefer_busy_poll)
+{
+ bool skip_schedule = false;
+ unsigned long timeout;
int rc;
/* Busy polling means there is a high chance device driver hard irq
@@ -6515,6 +6537,15 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock)
local_bh_disable();
+ if (prefer_busy_poll) {
+ napi->defer_hard_irqs_count = READ_ONCE(napi->dev->napi_defer_hard_irqs);
+ timeout = READ_ONCE(napi->dev->gro_flush_timeout);
+ if (napi->defer_hard_irqs_count && timeout) {
+ hrtimer_start(&napi->timer, ns_to_ktime(timeout), HRTIMER_MODE_REL_PINNED);
+ skip_schedule = true;
+ }
+ }
+
/* All we really want here is to re-enable device interrupts.
* Ideally, a new ndo_busy_poll_stop() could avoid another round.
*/
@@ -6525,19 +6556,14 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock)
*/
trace_napi_poll(napi, rc, BUSY_POLL_BUDGET);
netpoll_poll_unlock(have_poll_lock);
- if (rc == BUSY_POLL_BUDGET) {
- /* As the whole budget was spent, we still own the napi so can
- * safely handle the rx_list.
- */
- gro_normal_list(napi);
- __napi_schedule(napi);
- }
+ if (rc == BUSY_POLL_BUDGET)
+ __busy_poll_stop(napi, skip_schedule);
local_bh_enable();
}
void napi_busy_loop(unsigned int napi_id,
bool (*loop_end)(void *, unsigned long),
- void *loop_end_arg)
+ void *loop_end_arg, bool prefer_busy_poll)
{
unsigned long start_time = loop_end ? busy_loop_current_time() : 0;
int (*napi_poll)(struct napi_struct *napi, int budget);
@@ -6565,12 +6591,18 @@ void napi_busy_loop(unsigned int napi_id,
* we avoid dirtying napi->state as much as we can.
*/
if (val & (NAPIF_STATE_DISABLE | NAPIF_STATE_SCHED |
- NAPIF_STATE_IN_BUSY_POLL))
+ NAPIF_STATE_IN_BUSY_POLL)) {
+ if (prefer_busy_poll)
+ set_bit(NAPI_STATE_PREFER_BUSY_POLL, &napi->state);
goto count;
+ }
if (cmpxchg(&napi->state, val,
val | NAPIF_STATE_IN_BUSY_POLL |
- NAPIF_STATE_SCHED) != val)
+ NAPIF_STATE_SCHED) != val) {
+ if (prefer_busy_poll)
+ set_bit(NAPI_STATE_PREFER_BUSY_POLL, &napi->state);
goto count;
+ }
have_poll_lock = netpoll_poll_lock(napi);
napi_poll = napi->poll;
}
@@ -6588,7 +6620,7 @@ void napi_busy_loop(unsigned int napi_id,
if (unlikely(need_resched())) {
if (napi_poll)
- busy_poll_stop(napi, have_poll_lock);
+ busy_poll_stop(napi, have_poll_lock, prefer_busy_poll);
preempt_enable();
rcu_read_unlock();
cond_resched();
@@ -6599,7 +6631,7 @@ void napi_busy_loop(unsigned int napi_id,
cpu_relax();
}
if (napi_poll)
- busy_poll_stop(napi, have_poll_lock);
+ busy_poll_stop(napi, have_poll_lock, prefer_busy_poll);
preempt_enable();
out:
rcu_read_unlock();
@@ -6650,8 +6682,10 @@ static enum hrtimer_restart napi_watchdog(struct hrtimer *timer)
* NAPI_STATE_MISSED, since we do not react to a device IRQ.
*/
if (!napi_disable_pending(napi) &&
- !test_and_set_bit(NAPI_STATE_SCHED, &napi->state))
+ !test_and_set_bit(NAPI_STATE_SCHED, &napi->state)) {
+ clear_bit(NAPI_STATE_PREFER_BUSY_POLL, &napi->state);
__napi_schedule_irqoff(napi);
+ }
return HRTIMER_NORESTART;
}
@@ -6709,6 +6743,7 @@ void napi_disable(struct napi_struct *n)
hrtimer_cancel(&n->timer);
+ clear_bit(NAPI_STATE_PREFER_BUSY_POLL, &n->state);
clear_bit(NAPI_STATE_DISABLE, &n->state);
}
EXPORT_SYMBOL(napi_disable);
@@ -6781,6 +6816,19 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
goto out_unlock;
}
+ /* The NAPI context has more processing work, but busy-polling
+ * is preferred. Exit early.
+ */
+ if (napi_prefer_busy_poll(n)) {
+ if (napi_complete_done(n, work)) {
+ /* If timeout is not set, we need to make sure
+ * that the NAPI is re-scheduled.
+ */
+ napi_schedule(n);
+ }
+ goto out_unlock;
+ }
+
if (n->gro_bitmask) {
/* flush too old packets
* If HZ < 1000, flush all packets.
diff --git a/net/core/sock.c b/net/core/sock.c
index 727ea1cc633c..e05f2e52b5a8 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -1159,6 +1159,12 @@ int sock_setsockopt(struct socket *sock, int level, int optname,
sk->sk_ll_usec = val;
}
break;
+ case SO_PREFER_BUSY_POLL:
+ if (valbool && !capable(CAP_NET_ADMIN))
+ ret = -EPERM;
+ else
+ WRITE_ONCE(sk->sk_prefer_busy_poll, valbool);
+ break;
#endif
case SO_MAX_PACING_RATE:
@@ -1523,6 +1529,9 @@ int sock_getsockopt(struct socket *sock, int level, int optname,
case SO_BUSY_POLL:
v.val = sk->sk_ll_usec;
break;
+ case SO_PREFER_BUSY_POLL:
+ v.val = READ_ONCE(sk->sk_prefer_busy_poll);
+ break;
#endif
case SO_MAX_PACING_RATE:
--
2.27.0
