[PATCH v1] net: af_packet: Use hrtimer to do the retire operation

[Xin Zhao]

In a system with high real-time requirements, the timeout mechanism of
ordinary timers with jiffies granularity is insufficient to meet the
demands for real-time performance. Meanwhile, the optimization of CPU
usage with af_packet is quite significant. Use hrtimer instead of timer
to help compensate for the shortcomings in real-time performance.
In HZ=100 or HZ=250 system, the update of TP_STATUS_USER is not real-time
enough, with fluctuations reaching over 8ms (on a system with HZ=250).
This is unacceptable in some high real-time systems that require timely
processing of network packets. By replacing it with hrtimer, if a timeout
of 2ms is set, the update of TP_STATUS_USER can be stabilized to within
3 ms.

Signed-off-by: Xin Zhao <jackzxcui1989@xxxxxxx>
---
 net/packet/af_packet.c | 20 +++++++++++---------
 net/packet/internal.h  |  4 ++--
 2 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index bc438d0d9..636b72bf6 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -203,7 +203,7 @@ static void prb_retire_current_block(struct tpacket_kbdq_core *,
 static int prb_queue_frozen(struct tpacket_kbdq_core *);
 static void prb_open_block(struct tpacket_kbdq_core *,
 		struct tpacket_block_desc *);
-static void prb_retire_rx_blk_timer_expired(struct timer_list *);
+static enum hrtimer_restart prb_retire_rx_blk_timer_expired(struct hrtimer *);
 static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *);
 static void prb_fill_rxhash(struct tpacket_kbdq_core *, struct tpacket3_hdr *);
 static void prb_clear_rxhash(struct tpacket_kbdq_core *,
@@ -581,7 +581,7 @@ static __be16 vlan_get_protocol_dgram(const struct sk_buff *skb)
 
 static void prb_del_retire_blk_timer(struct tpacket_kbdq_core *pkc)
 {
-	timer_delete_sync(&pkc->retire_blk_timer);
+	hrtimer_cancel(&pkc->retire_blk_timer);
 }
 
 static void prb_shutdown_retire_blk_timer(struct packet_sock *po,
@@ -603,9 +603,10 @@ static void prb_setup_retire_blk_timer(struct packet_sock *po)
 	struct tpacket_kbdq_core *pkc;
 
 	pkc = GET_PBDQC_FROM_RB(&po->rx_ring);
-	timer_setup(&pkc->retire_blk_timer, prb_retire_rx_blk_timer_expired,
-		    0);
-	pkc->retire_blk_timer.expires = jiffies;
+	hrtimer_setup(&pkc->retire_blk_timer, prb_retire_rx_blk_timer_expired,
+		      CLOCK_MONOTONIC, HRTIMER_MODE_REL_SOFT);
+	hrtimer_start(&pkc->retire_blk_timer, ms_to_ktime(pkc->tov_in_msecs),
+		      HRTIMER_MODE_REL_SOFT);
 }
 
 static int prb_calc_retire_blk_tmo(struct packet_sock *po,
@@ -676,7 +677,7 @@ static void init_prb_bdqc(struct packet_sock *po,
 	else
 		p1->retire_blk_tov = prb_calc_retire_blk_tmo(po,
 						req_u->req3.tp_block_size);
-	p1->tov_in_jiffies = msecs_to_jiffies(p1->retire_blk_tov);
+	p1->tov_in_msecs = p1->retire_blk_tov;
 	p1->blk_sizeof_priv = req_u->req3.tp_sizeof_priv;
 	rwlock_init(&p1->blk_fill_in_prog_lock);
 
@@ -691,8 +692,8 @@ static void init_prb_bdqc(struct packet_sock *po,
  */
 static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
 {
-	mod_timer(&pkc->retire_blk_timer,
-			jiffies + pkc->tov_in_jiffies);
+	hrtimer_set_expires(&pkc->retire_blk_timer,
+			    ktime_add(ktime_get(), ms_to_ktime(pkc->tov_in_msecs)));
 	pkc->last_kactive_blk_num = pkc->kactive_blk_num;
 }
 
@@ -719,7 +720,7 @@ static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc)
  * prb_calc_retire_blk_tmo() calculates the tmo.
  *
  */
-static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
+static enum hrtimer_restart prb_retire_rx_blk_timer_expired(struct hrtimer *t)
 {
 	struct packet_sock *po =
 		timer_container_of(po, t, rx_ring.prb_bdqc.retire_blk_timer);
@@ -790,6 +791,7 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
 
 out:
 	spin_unlock(&po->sk.sk_receive_queue.lock);
+	return HRTIMER_RESTART;
 }
 
 static void prb_flush_block(struct tpacket_kbdq_core *pkc1,
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 1e743d031..41df245e3 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -47,10 +47,10 @@ struct tpacket_kbdq_core {
 
 	unsigned short  retire_blk_tov;
 	unsigned short  version;
-	unsigned long	tov_in_jiffies;
+	unsigned long	tov_in_msecs;
 
 	/* timer to retire an outstanding block */
-	struct timer_list retire_blk_timer;
+	struct hrtimer retire_blk_timer;
 };
 
 struct pgv {
-- 
2.34.1