2024-12-10 00:17:37 +03:00
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From 9fd50b0891febee43126ba643bfe56f72dd23bad Mon Sep 17 00:00:00 2001
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2024-10-29 05:12:06 +03:00
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From: Neal Cardwell <ncardwell@google.com>
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Date: Sun, 24 Jun 2018 21:55:59 -0400
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Subject: [PATCH 02/19] net-tcp_bbr: v2: shrink delivered_mstamp,
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first_tx_mstamp to u32 to free up 8 bytes
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Free up some space for tracking inflight and losses for each
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bw sample, in upcoming commits.
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These timestamps are in microseconds, and are now stored in 32
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bits. So they can only hold time intervals up to roughly 2^12 = 4096
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seconds. But Linux TCP RTT and RTO tracking has the same 32-bit
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microsecond implementation approach and resulting deployment
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limitations. So this is not introducing a new limit. And these should
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not be a limitation for the foreseeable future.
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Effort: net-tcp_bbr
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Origin-9xx-SHA1: 238a7e6b5d51625fef1ce7769826a7b21b02ae55
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Change-Id: I3b779603797263b52a61ad57c565eb91fe42680c
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Signed-off-by: Alexandre Frade <kernel@xanmod.org>
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---
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include/net/tcp.h | 9 +++++++--
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net/ipv4/tcp_rate.c | 7 ++++---
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2 files changed, 11 insertions(+), 5 deletions(-)
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--- a/include/net/tcp.h
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+++ b/include/net/tcp.h
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@@ -884,6 +884,11 @@ static inline u32 tcp_stamp_us_delta(u64
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return max_t(s64, t1 - t0, 0);
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}
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+static inline u32 tcp_stamp32_us_delta(u32 t1, u32 t0)
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+{
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+ return max_t(s32, t1 - t0, 0);
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+}
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+
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/* provide the departure time in us unit */
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static inline u64 tcp_skb_timestamp_us(const struct sk_buff *skb)
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{
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@@ -973,9 +978,9 @@ struct tcp_skb_cb {
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/* pkts S/ACKed so far upon tx of skb, incl retrans: */
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__u32 delivered;
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/* start of send pipeline phase */
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- u64 first_tx_mstamp;
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+ u32 first_tx_mstamp;
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/* when we reached the "delivered" count */
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- u64 delivered_mstamp;
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+ u32 delivered_mstamp;
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} tx; /* only used for outgoing skbs */
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union {
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struct inet_skb_parm h4;
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--- a/net/ipv4/tcp_rate.c
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+++ b/net/ipv4/tcp_rate.c
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@@ -101,8 +101,9 @@ void tcp_rate_skb_delivered(struct sock
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/* Record send time of most recently ACKed packet: */
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tp->first_tx_mstamp = tx_tstamp;
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/* Find the duration of the "send phase" of this window: */
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- rs->interval_us = tcp_stamp_us_delta(tp->first_tx_mstamp,
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- scb->tx.first_tx_mstamp);
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+ rs->interval_us = tcp_stamp32_us_delta(
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+ tp->first_tx_mstamp,
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+ scb->tx.first_tx_mstamp);
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}
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/* Mark off the skb delivered once it's sacked to avoid being
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@@ -155,7 +156,7 @@ void tcp_rate_gen(struct sock *sk, u32 d
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* longer phase.
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*/
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snd_us = rs->interval_us; /* send phase */
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- ack_us = tcp_stamp_us_delta(tp->tcp_mstamp,
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+ ack_us = tcp_stamp32_us_delta(tp->tcp_mstamp,
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rs->prior_mstamp); /* ack phase */
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rs->interval_us = max(snd_us, ack_us);
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