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Message-Id: <20250816170130.3969354-1-jackzxcui1989@163.com>
Date: Sun, 17 Aug 2025 01:01:30 +0800
From: Xin Zhao <jackzxcui1989@....com>
To: willemdebruijn.kernel@...il.com,
edumazet@...gle.com,
ferenc@...es.dev
Cc: davem@...emloft.net,
kuba@...nel.org,
pabeni@...hat.com,
horms@...nel.org,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
Xin Zhao <jackzxcui1989@....com>
Subject: [PATCH net-next v3] net: af_packet: Use hrtimer to do the retire operation
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@....com>
---
Changes in v3:
- return HRTIMER_NORESTART when pkc->delete_blk_timer is true
as suggested by Willem de Bruijn;
- Drop the retire_blk_tov field of tpacket_kbdq_core, add interval_ktime instead
as suggested by Willem de Bruijn;
- Add comments to explain why hrtimer_set_expires(not hrtimer_forward_now) is used in
_prb_refresh_rx_retire_blk_timer
as suggested by Willem de Bruijn;
Changes in v2:
- Drop the tov_in_msecs field of tpacket_kbdq_core added by the patch
as suggested by Willem de Bruijn;
- Link to v2: https://lore.kernel.org/all/20250815044141.1374446-1-jackzxcui1989@163.com/
Changes in v1:
- Do not add another config for the current changes
as suggested by Eric Dumazet;
- Mention the beneficial cases 'HZ=100 or HZ=250' in the changelog
as suggested by Eric Dumazet;
- Add some performance details to the changelog
as suggested by Ferenc Fejes;
- Delete the 'pkc->tov_in_msecs == 0' bounds check which is not necessary
as suggested by Willem de Bruijn;
- Use hrtimer_set_expires instead of hrtimer_start_range_ns when retire timer needs update
as suggested by Willem de Bruijn. Start the hrtimer in prb_setup_retire_blk_timer;
- Just return HRTIMER_RESTART directly as all cases return the same value
as suggested by Willem de Bruijn;
- Link to v1: https://lore.kernel.org/all/20250813165201.1492779-1-jackzxcui1989@163.com/
- Link to v0: https://lore.kernel.org/all/20250806055210.1530081-1-jackzxcui1989@163.com/
---
---
net/packet/af_packet.c | 39 ++++++++++++++++++++++++++-------------
net/packet/diag.c | 2 +-
net/packet/internal.h | 5 ++---
3 files changed, 29 insertions(+), 17 deletions(-)
diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index a7017d7f0..11b3d2cfa 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, pkc->interval_ktime,
+ HRTIMER_MODE_REL_SOFT);
}
static int prb_calc_retire_blk_tmo(struct packet_sock *po,
@@ -672,11 +673,10 @@ static void init_prb_bdqc(struct packet_sock *po,
p1->last_kactive_blk_num = 0;
po->stats.stats3.tp_freeze_q_cnt = 0;
if (req_u->req3.tp_retire_blk_tov)
- p1->retire_blk_tov = req_u->req3.tp_retire_blk_tov;
+ p1->interval_ktime = ms_to_ktime(req_u->req3.tp_retire_blk_tov);
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->interval_ktime = ms_to_ktime(prb_calc_retire_blk_tmo(po,
+ req_u->req3.tp_block_size));
p1->blk_sizeof_priv = req_u->req3.tp_sizeof_priv;
rwlock_init(&p1->blk_fill_in_prog_lock);
@@ -691,8 +691,17 @@ 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);
+ /* We cannot use hrtimer_forward_now here because the function
+ * _prb_refresh_rx_retire_blk_timer can be called not only when
+ * the retire timer expires, but also when the kernel logic for
+ * receiving network packets detects that a network packet has
+ * filled up a block and calls prb_open_block to use the next
+ * block. This can lead to a WARN_ON being triggered in
+ * hrtimer_forward_now when it checks if the timer has already
+ * been enqueued.
+ */
+ hrtimer_set_expires(&pkc->retire_blk_timer,
+ ktime_add(ktime_get(), pkc->interval_ktime));
pkc->last_kactive_blk_num = pkc->kactive_blk_num;
}
@@ -719,8 +728,9 @@ 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)
{
+ enum hrtimer_restart ret = HRTIMER_RESTART;
struct packet_sock *po =
timer_container_of(po, t, rx_ring.prb_bdqc.retire_blk_timer);
struct tpacket_kbdq_core *pkc = GET_PBDQC_FROM_RB(&po->rx_ring);
@@ -732,8 +742,10 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
frozen = prb_queue_frozen(pkc);
pbd = GET_CURR_PBLOCK_DESC_FROM_CORE(pkc);
- if (unlikely(pkc->delete_blk_timer))
+ if (unlikely(pkc->delete_blk_timer)) {
+ ret = HRTIMER_NORESTART;
goto out;
+ }
/* We only need to plug the race when the block is partially filled.
* tpacket_rcv:
@@ -790,6 +802,7 @@ static void prb_retire_rx_blk_timer_expired(struct timer_list *t)
out:
spin_unlock(&po->sk.sk_receive_queue.lock);
+ return ret;
}
static void prb_flush_block(struct tpacket_kbdq_core *pkc1,
diff --git a/net/packet/diag.c b/net/packet/diag.c
index 6ce1dcc28..c8f43e0c1 100644
--- a/net/packet/diag.c
+++ b/net/packet/diag.c
@@ -83,7 +83,7 @@ static int pdiag_put_ring(struct packet_ring_buffer *ring, int ver, int nl_type,
pdr.pdr_frame_nr = ring->frame_max + 1;
if (ver > TPACKET_V2) {
- pdr.pdr_retire_tmo = ring->prb_bdqc.retire_blk_tov;
+ pdr.pdr_retire_tmo = ktime_to_ms(ring->prb_bdqc.interval_ktime);
pdr.pdr_sizeof_priv = ring->prb_bdqc.blk_sizeof_priv;
pdr.pdr_features = ring->prb_bdqc.feature_req_word;
} else {
diff --git a/net/packet/internal.h b/net/packet/internal.h
index 1e743d031..19d4f0b73 100644
--- a/net/packet/internal.h
+++ b/net/packet/internal.h
@@ -45,12 +45,11 @@ struct tpacket_kbdq_core {
/* Default is set to 8ms */
#define DEFAULT_PRB_RETIRE_TOV (8)
- unsigned short retire_blk_tov;
+ ktime_t interval_ktime;
unsigned short version;
- unsigned long tov_in_jiffies;
/* timer to retire an outstanding block */
- struct timer_list retire_blk_timer;
+ struct hrtimer retire_blk_timer;
};
struct pgv {
--
2.34.1
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