diff options
author | Hechao Li <hli@netflix.com> | 2024-04-09 19:43:55 +0300 |
---|---|---|
committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2024-05-30 10:44:20 +0300 |
commit | 43bfd1952216d240d22810e4adc323c32cf64223 (patch) | |
tree | 890b0cabae2500cd506b97942c7867312f578239 | |
parent | 989b8f3104c2fbc747d497c0c2424ef0c2916a42 (diff) | |
download | linux-43bfd1952216d240d22810e4adc323c32cf64223.tar.xz |
tcp: increase the default TCP scaling ratio
[ Upstream commit 697a6c8cec03c2299f850fa50322641a8bf6b915 ]
After commit dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale"),
we noticed an application-level timeout due to reduced throughput.
Before the commit, for a client that sets SO_RCVBUF to 65k, it takes
around 22 seconds to transfer 10M data. After the commit, it takes 40
seconds. Because our application has a 30-second timeout, this
regression broke the application.
The reason that it takes longer to transfer data is that
tp->scaling_ratio is initialized to a value that results in ~0.25 of
rcvbuf. In our case, SO_RCVBUF is set to 65536 by the application, which
translates to 2 * 65536 = 131,072 bytes in rcvbuf and hence a ~28k
initial receive window.
Later, even though the scaling_ratio is updated to a more accurate
skb->len/skb->truesize, which is ~0.66 in our environment, the window
stays at ~0.25 * rcvbuf. This is because tp->window_clamp does not
change together with the tp->scaling_ratio update when autotuning is
disabled due to SO_RCVBUF. As a result, the window size is capped at the
initial window_clamp, which is also ~0.25 * rcvbuf, and never grows
bigger.
Most modern applications let the kernel do autotuning, and benefit from
the increased scaling_ratio. But there are applications such as kafka
that has a default setting of SO_RCVBUF=64k.
This patch increases the initial scaling_ratio from ~25% to 50% in order
to make it backward compatible with the original default
sysctl_tcp_adv_win_scale for applications setting SO_RCVBUF.
Fixes: dfa2f0483360 ("tcp: get rid of sysctl_tcp_adv_win_scale")
Signed-off-by: Hechao Li <hli@netflix.com>
Reviewed-by: Tycho Andersen <tycho@tycho.pizza>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Link: https://lore.kernel.org/netdev/20240402215405.432863-1-hli@netflix.com/
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>
-rw-r--r-- | include/net/tcp.h | 5 |
1 files changed, 2 insertions, 3 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h index 6ae35199d3b3..2bcf30381d75 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1539,11 +1539,10 @@ static inline int tcp_space_from_win(const struct sock *sk, int win) return __tcp_space_from_win(tcp_sk(sk)->scaling_ratio, win); } -/* Assume a conservative default of 1200 bytes of payload per 4K page. +/* Assume a 50% default for skb->len/skb->truesize ratio. * This may be adjusted later in tcp_measure_rcv_mss(). */ -#define TCP_DEFAULT_SCALING_RATIO ((1200 << TCP_RMEM_TO_WIN_SCALE) / \ - SKB_TRUESIZE(4096)) +#define TCP_DEFAULT_SCALING_RATIO (1 << (TCP_RMEM_TO_WIN_SCALE - 1)) static inline void tcp_scaling_ratio_init(struct sock *sk) { |