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CLEANUP: quic: no need for atomics on packet refcnt

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This is a leftover from the implementation's history, but the
quic_rx_packet and quic_tx_packet ref counts were still atomically
updated. It was found in perf top that the cost of the atomic inc
in quic_tx_packet_refinc() alone was responsible for 1% of the CPU
usage at 135 Gbps. Given that packets are only processed on their
assigned thread we don't need that anymore and this can be replaced
with regular non-atomic operations.

Doing this alone has reduced the CPU usage of qc_do_build_pkt()
from 3.6 to 2.5% and increased the overall bit rate by about 1%.
This commit is contained in:
Willy Tarreau 2023-02-02 15:37:24 +01:00
parent 23aa79d9a9
commit 1ea5f410ff
1 changed files with 6 additions and 9 deletions
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15
include/haproxy/quic_conn.h
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@ -502,13 +502,13 @@ static inline void quic_tx_packet_dgram_detach(struct quic_tx_packet *pkt)
/* Increment the reference counter of <pkt> */ /* Increment the reference counter of <pkt> */
static inline void quic_tx_packet_refinc(struct quic_tx_packet *pkt) static inline void quic_tx_packet_refinc(struct quic_tx_packet *pkt)
{ {
HA_ATOMIC_ADD(&pkt->refcnt, 1); pkt->refcnt++;
} }
/* Decrement the reference counter of <pkt> */ /* Decrement the reference counter of <pkt> */
static inline void quic_tx_packet_refdec(struct quic_tx_packet *pkt) static inline void quic_tx_packet_refdec(struct quic_tx_packet *pkt)
{ {
if (!HA_ATOMIC_SUB_FETCH(&pkt->refcnt, 1)) { if (--pkt->refcnt == 0) {
BUG_ON(!LIST_ISEMPTY(&pkt->frms)); BUG_ON(!LIST_ISEMPTY(&pkt->frms));
/* If there are others packet in the same datagram <pkt> is attached to, /* If there are others packet in the same datagram <pkt> is attached to,
* detach the previous one and the next one from <pkt>. * detach the previous one and the next one from <pkt>.
@ -670,7 +670,7 @@ static inline void quic_rx_pkts_del(struct quic_conn *qc)
break; break;
} }
if (HA_ATOMIC_LOAD(&pkt->refcnt)) if (pkt->refcnt)
break; break;
b_del(&qc->rx.buf, pkt->raw_len); b_del(&qc->rx.buf, pkt->raw_len);
@ -685,17 +685,14 @@ static inline void quic_rx_pkts_del(struct quic_conn *qc)
/* Increment the reference counter of <pkt> */ /* Increment the reference counter of <pkt> */
static inline void quic_rx_packet_refinc(struct quic_rx_packet *pkt) static inline void quic_rx_packet_refinc(struct quic_rx_packet *pkt)
{ {
HA_ATOMIC_ADD(&pkt->refcnt, 1); pkt->refcnt++;
} }
/* Decrement the reference counter of <pkt> while remaining positive */ /* Decrement the reference counter of <pkt> while remaining positive */
static inline void quic_rx_packet_refdec(struct quic_rx_packet *pkt) static inline void quic_rx_packet_refdec(struct quic_rx_packet *pkt)
{ {
unsigned int refcnt; if (pkt->refcnt)
pkt->refcnt--;
do {
refcnt = HA_ATOMIC_LOAD(&pkt->refcnt);
} while (refcnt && !HA_ATOMIC_CAS(&pkt->refcnt, &refcnt, refcnt - 1));
} }
/* Delete all RX packets for <qel> QUIC encryption level */ /* Delete all RX packets for <qel> QUIC encryption level */