CLEANUP: quic: no need for atomics on packet refcnt

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%.

diff --git a/include/haproxy/quic_conn.h b/include/haproxy/quic_conn.h
index 60afccd8deb086527afdd69c2c165123e758d199..b5f25d865ceeb17bbeace8617f49a6f36632c2f6 100644 (file)
--- a/include/haproxy/quic_conn.h
+++ b/include/haproxy/quic_conn.h
@@ -502,13 +502,13 @@ static inline void quic_tx_packet_dgram_detach(struct quic_tx_packet *pkt)
 /* Increment the reference counter of <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> */
 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));
                /* If there are others packet in the same datagram <pkt> is attached to,
                 * 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;
                }
 
-               if (HA_ATOMIC_LOAD(&pkt->refcnt))
+               if (pkt->refcnt)
                        break;
 
                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> */
 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 */
 static inline void quic_rx_packet_refdec(struct quic_rx_packet *pkt)
 {
-       unsigned int refcnt;
-
-       do {
-               refcnt = HA_ATOMIC_LOAD(&pkt->refcnt);
-       } while (refcnt && !HA_ATOMIC_CAS(&pkt->refcnt, &refcnt, refcnt - 1));
+       if (pkt->refcnt)
+               pkt->refcnt--;
 }
 
 /* Delete all RX packets for <qel> QUIC encryption level */