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(unknown []) by gzsmtp5 (Coremail) with SMTP id QCgvCgCH5M3OHa9owOQpAw--.53765S2; Wed, 27 Aug 2025 23:01:35 +0800 (CST) From: Xin Zhao To: willemdebruijn.kernel@gmail.com, edumazet@google.com, ferenc@fejes.dev Cc: davem@davemloft.net, kuba@kernel.org, pabeni@redhat.com, horms@kernel.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Xin Zhao Subject: [PATCH net-next v8] net: af_packet: Use hrtimer to do the retire operation Date: Wed, 27 Aug 2025 23:01:31 +0800 Message-Id: <20250827150131.2193485-1-jackzxcui1989@163.com> X-Mailer: git-send-email 2.34.1 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-CM-TRANSID: QCgvCgCH5M3OHa9owOQpAw--.53765S2 X-Coremail-Antispam: 1Uf129KBjvAXoW3uw4xCF4kAF15Xry8tw4UCFg_yoW8GF18Go Z3XrZ8Cr4kAFy7A3ykCFyIkFy3W3yqqr15Jr4F9r1ku3Z2vw15Wr17Aayaq3yfCw1Syw1q yF18W34UXF1Dtr1rn29KB7ZKAUJUUUU8529EdanIXcx71UUUUU7v73VFW2AGmfu7bjvjm3 AaLaJ3UbIYCTnIWIevJa73UjIFyTuYvjTR3Ks0DUUUU X-CM-SenderInfo: pmdfy650fxxiqzyzqiywtou0bp/1tbibga2CmivGPZ4twAAsy Content-Type: text/plain; charset="utf-8" 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=3D100 or HZ=3D250 system, the update of TP_STATUS_USER is not real-ti= me enough, with fluctuations reaching over 8ms (on a system with HZ=3D250). 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 --- Changes in v8: - Delete delete_blk_timer field, as suggested by Willem de Bruijn, hrtimer_cancel will check and wait until the timer callback return and en= sure enter enter callback again; - Simplify the logic related to setting timeout, as suggestd by Willem de B= ruijn. Currently timer callback just restarts itself unconditionally, so delete = the 'out:' label, do not forward hrtimer in prb_open_block, call hrtimer_forwa= rd_now directly and always return HRTIMER_RESTART. The only special case is when prb_open_block is called from tpacket_rcv. That would set the timeout fur= ther into the future than the already queued timer. An earlier timeout is not problematic. No need to add complexity to avoid that. Changes in v7: - Only update the hrtimer expire time within the hrtimer callback. When the callback return, without sk_buff_head lock protection, __run_hrt= imer will enqueue the timer if return HRTIMER_RESTART. Setting the hrtimer expires = while enqueuing a timer may cause chaos in the hrtimer red-black tree. The setting expire time is monotonic, so if we do not update the expire t= ime to the retire_blk_timer when it is not in callback, it will not cause problem if= we skip the timeout event and update it when find out that expire_ktime is bigger= than the expire time of retire_blk_timer. - Use hrtimer_set_expires instead of hrtimer_forward_now. The end time for retiring each block is not fixed because when network pa= ckets are received quickly, blocks are retired rapidly, and the new block retire ti= me needs to be recalculated. However, hrtimer_forward_now increments the previous = timeout by an interval, which is not correct. - The expire time is monotonic, so if we do not update the expire time to t= he retire_blk_timer when it is not in callback, it will not cause problem if= we skip the timeout event and update it when find out that expire_ktime is bigger= than the expire time of retire_blk_timer. - Adding the 'bool callback' parameter back is intended to more accurately = determine whether we are inside the hrtimer callback when executing _prb_refresh_rx_retire_blk_timer. This ensures that we only update the hr= timer's timeout value within the hrtimer callback. - Link to v7: https://lore.kernel.org/all/20250822132051.266787-1-jackzxcui= 1989@163.com/ Changes in v6: - Use hrtimer_is_queued instead to check whether it is within the callback = function. So do not need to add 'bool callback' parameter to _prb_refresh_rx_retire= _blk_timer as suggested by Willem de Bruijn; - Do not need local_irq_save and local_irq_restore to protect the race of t= he timer callback running in softirq context or the open_block from tpacket_rcv in= process context as suggested by Willem de Bruijn; - Link to v6: https://lore.kernel.org/all/20250820092925.2115372-1-jackzxcu= i1989@163.com/ Changes in v5: - Remove the unnecessary comments at the top of the _prb_refresh_rx_retire_= blk_timer, branch is self-explanatory enough as suggested by Willem de Bruijn; - Indentation of _prb_refresh_rx_retire_blk_timer, align with first argumen= t on previous line as suggested by Willem de Bruijn; - Do not call hrtimer_start within the hrtimer callback as suggested by Willem de Bruijn So add 'bool callback' parameter to _prb_refresh_rx_retire_blk_timer to i= ndicate whether it is within the callback function. Use hrtimer_forward_now inste= ad of hrtimer_start when it is in the callback function and is doing prb_open_b= lock. - Link to v5: https://lore.kernel.org/all/20250819091447.1199980-1-jackzxcu= i1989@163.com/ Changes in v4: - Add 'bool start' to distinguish whether the call to _prb_refresh_rx_retir= e_blk_timer is for prb_open_block. When it is for prb_open_block, execute hrtimer_sta= rt to (re)start the hrtimer; otherwise, use hrtimer_forward_now to set the expi= ration time as it is more commonly used compared to hrtimer_set_expires. as suggested by Willem de Bruijn; - Delete the comments to explain why hrtimer_set_expires(not hrtimer_forwar= d_now) is used, as we do not use hrtimer_set_expires any more; - Link to v4: https://lore.kernel.org/all/20250818050233.155344-1-jackzxcui= 1989@163.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 in= stead 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; - Link to v3: https://lore.kernel.org/all/20250816170130.3969354-1-jackzxcu= i1989@163.com/ 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-jackzxcu= i1989@163.com/ Changes in v1: - Do not add another config for the current changes as suggested by Eric Dumazet; - Mention the beneficial cases 'HZ=3D100 or HZ=3D250' 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 =3D=3D 0' bounds check which is not necessa= ry as suggested by Willem de Bruijn; - Use hrtimer_set_expires instead of hrtimer_start_range_ns when retire tim= er needs update as suggested by Willem de Bruijn. Start the hrtimer in prb_setup_retire_b= lk_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-jackzxcu= i1989@163.com/ - Link to v0: https://lore.kernel.org/all/20250806055210.1530081-1-jackzxcu= i1989@163.com/ --- net/packet/af_packet.c | 65 ++++++++++-------------------------------- net/packet/diag.c | 2 +- net/packet/internal.h | 6 ++-- 3 files changed, 18 insertions(+), 55 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index a7017d7f0..bf1127d87 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -203,8 +203,7 @@ static void prb_retire_current_block(struct tpacket_kbd= q_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 void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *); +static enum hrtimer_restart prb_retire_rx_blk_timer_expired(struct hrtimer= *); static void prb_fill_rxhash(struct tpacket_kbdq_core *, struct tpacket3_hd= r *); static void prb_clear_rxhash(struct tpacket_kbdq_core *, struct tpacket3_hdr *); @@ -579,23 +578,13 @@ static __be16 vlan_get_protocol_dgram(const struct sk= _buff *skb) return proto; } =20 -static void prb_del_retire_blk_timer(struct tpacket_kbdq_core *pkc) -{ - timer_delete_sync(&pkc->retire_blk_timer); -} - static void prb_shutdown_retire_blk_timer(struct packet_sock *po, struct sk_buff_head *rb_queue) { struct tpacket_kbdq_core *pkc; =20 pkc =3D GET_PBDQC_FROM_RB(&po->rx_ring); - - spin_lock_bh(&rb_queue->lock); - pkc->delete_blk_timer =3D 1; - spin_unlock_bh(&rb_queue->lock); - - prb_del_retire_blk_timer(pkc); + hrtimer_cancel(&pkc->retire_blk_timer); } =20 static void prb_setup_retire_blk_timer(struct packet_sock *po) @@ -603,9 +592,10 @@ static void prb_setup_retire_blk_timer(struct packet_s= ock *po) struct tpacket_kbdq_core *pkc; =20 pkc =3D 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 =3D 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); } =20 static int prb_calc_retire_blk_tmo(struct packet_sock *po, @@ -672,11 +662,10 @@ static void init_prb_bdqc(struct packet_sock *po, p1->last_kactive_blk_num =3D 0; po->stats.stats3.tp_freeze_q_cnt =3D 0; if (req_u->req3.tp_retire_blk_tov) - p1->retire_blk_tov =3D req_u->req3.tp_retire_blk_tov; + p1->interval_ktime =3D ms_to_ktime(req_u->req3.tp_retire_blk_tov); else - p1->retire_blk_tov =3D prb_calc_retire_blk_tmo(po, - req_u->req3.tp_block_size); - p1->tov_in_jiffies =3D msecs_to_jiffies(p1->retire_blk_tov); + p1->interval_ktime =3D ms_to_ktime(prb_calc_retire_blk_tmo(po, + req_u->req3.tp_block_size)); p1->blk_sizeof_priv =3D req_u->req3.tp_sizeof_priv; rwlock_init(&p1->blk_fill_in_prog_lock); =20 @@ -686,16 +675,6 @@ static void init_prb_bdqc(struct packet_sock *po, prb_open_block(p1, pbd); } =20 -/* Do NOT update the last_blk_num first. - * Assumes sk_buff_head lock is held. - */ -static void _prb_refresh_rx_retire_blk_timer(struct tpacket_kbdq_core *pkc) -{ - mod_timer(&pkc->retire_blk_timer, - jiffies + pkc->tov_in_jiffies); - pkc->last_kactive_blk_num =3D pkc->kactive_blk_num; -} - /* * Timer logic: * 1) We refresh the timer only when we open a block. @@ -719,7 +698,7 @@ static void _prb_refresh_rx_retire_blk_timer(struct tpa= cket_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 =3D timer_container_of(po, t, rx_ring.prb_bdqc.retire_blk_timer); @@ -732,9 +711,6 @@ static void prb_retire_rx_blk_timer_expired(struct time= r_list *t) frozen =3D prb_queue_frozen(pkc); pbd =3D GET_CURR_PBLOCK_DESC_FROM_CORE(pkc); =20 - if (unlikely(pkc->delete_blk_timer)) - goto out; - /* We only need to plug the race when the block is partially filled. * tpacket_rcv: * lock(); increment BLOCK_NUM_PKTS; unlock() @@ -757,21 +733,12 @@ static void prb_retire_rx_blk_timer_expired(struct ti= mer_list *t) goto refresh_timer; } prb_retire_current_block(pkc, po, TP_STATUS_BLK_TMO); - if (!prb_dispatch_next_block(pkc, po)) - goto refresh_timer; - else - goto out; + prb_dispatch_next_block(pkc, po); } else { /* Case 1. Queue was frozen because user-space was * lagging behind. */ - if (prb_curr_blk_in_use(pbd)) { - /* - * Ok, user-space is still behind. - * So just refresh the timer. - */ - goto refresh_timer; - } else { + if (!prb_curr_blk_in_use(pbd)) { /* Case 2. queue was frozen,user-space caught up, * now the link went idle && the timer fired. * We don't have a block to close.So we open this @@ -780,16 +747,14 @@ static void prb_retire_rx_blk_timer_expired(struct ti= mer_list *t) * Thawing/timer-refresh is a side effect. */ prb_open_block(pkc, pbd); - goto out; } } } =20 refresh_timer: - _prb_refresh_rx_retire_blk_timer(pkc); - -out: + hrtimer_forward_now(&pkc->retire_blk_timer, pkc->interval_ktime); spin_unlock(&po->sk.sk_receive_queue.lock); + return HRTIMER_RESTART; } =20 static void prb_flush_block(struct tpacket_kbdq_core *pkc1, @@ -921,7 +886,7 @@ static void prb_open_block(struct tpacket_kbdq_core *pk= c1, pkc1->pkblk_end =3D pkc1->pkblk_start + pkc1->kblk_size; =20 prb_thaw_queue(pkc1); - _prb_refresh_rx_retire_blk_timer(pkc1); + pkc1->last_kactive_blk_num =3D pkc1->kactive_blk_num; =20 smp_wmb(); } 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 =3D ring->frame_max + 1; =20 if (ver > TPACKET_V2) { - pdr.pdr_retire_tmo =3D ring->prb_bdqc.retire_blk_tov; + pdr.pdr_retire_tmo =3D ktime_to_ms(ring->prb_bdqc.interval_ktime); pdr.pdr_sizeof_priv =3D ring->prb_bdqc.blk_sizeof_priv; pdr.pdr_features =3D ring->prb_bdqc.feature_req_word; } else { diff --git a/net/packet/internal.h b/net/packet/internal.h index 1e743d031..30ae8979f 100644 --- a/net/packet/internal.h +++ b/net/packet/internal.h @@ -20,7 +20,6 @@ struct tpacket_kbdq_core { unsigned int feature_req_word; unsigned int hdrlen; unsigned char reset_pending_on_curr_blk; - unsigned char delete_blk_timer; unsigned short kactive_blk_num; unsigned short blk_sizeof_priv; =20 @@ -45,12 +44,11 @@ struct tpacket_kbdq_core { /* Default is set to 8ms */ #define DEFAULT_PRB_RETIRE_TOV (8) =20 - unsigned short retire_blk_tov; + ktime_t interval_ktime; unsigned short version; - unsigned long tov_in_jiffies; =20 /* timer to retire an outstanding block */ - struct timer_list retire_blk_timer; + struct hrtimer retire_blk_timer; }; =20 struct pgv { --=20 2.34.1