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| author | Andrew Shewmaker <agshew@gmail.com> | 2015-10-18 21:59:08 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-10-23 02:46:52 -0700 |
| commit | c80dbe04612986fd6104b4a1be21681b113b5ac9 (patch) | |
| tree | a0ddb2c94d317b163b2c5a5dbff06cf6534d1f94 | |
| parent | ab997ad408394bcaf7f3015d4c4e38047eaf2ad6 (diff) | |
| download | op-kernel-dev-c80dbe04612986fd6104b4a1be21681b113b5ac9.zip op-kernel-dev-c80dbe04612986fd6104b4a1be21681b113b5ac9.tar.gz | |
tcp: allow dctcp alpha to drop to zero
If alpha is strictly reduced by alpha >> dctcp_shift_g and if alpha is less
than 1 << dctcp_shift_g, then alpha may never reach zero. For example,
given shift_g=4 and alpha=15, alpha >> dctcp_shift_g yields 0 and alpha
remains 15. The effect isn't noticeable in this case below cwnd=137, but
could gradually drive uncongested flows with leftover alpha down to
cwnd=137. A larger dctcp_shift_g would have a greater effect.
This change causes alpha=15 to drop to 0 instead of being decrementing by 1
as it would when alpha=16. However, it requires one less conditional to
implement since it doesn't have to guard against subtracting 1 from 0U. A
decay of 15 is not unreasonable since an equal or greater amount occurs at
alpha >= 240.
Signed-off-by: Andrew G. Shewmaker <agshew@gmail.com>
Acked-by: Florian Westphal <fw@strlen.de>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | net/ipv4/tcp_dctcp.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/net/ipv4/tcp_dctcp.c b/net/ipv4/tcp_dctcp.c index 7092a61..7e538f7 100644 --- a/net/ipv4/tcp_dctcp.c +++ b/net/ipv4/tcp_dctcp.c @@ -209,7 +209,7 @@ static void dctcp_update_alpha(struct sock *sk, u32 flags) /* alpha = (1 - g) * alpha + g * F */ - alpha -= alpha >> dctcp_shift_g; + alpha -= min_not_zero(alpha, alpha >> dctcp_shift_g); if (bytes_ecn) { /* If dctcp_shift_g == 1, a 32bit value would overflow * after 8 Mbytes. |
