| From | Greg Kroah-Hartman <> | Subject | [ 001/262] codel: refine one condition to avoid a nul rec_inv_sqrt | Date | Fri, 28 Sep 2012 11:48:50 -0700 |
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From: Greg KH <gregkh@linuxfoundation.org>
3.5-stable review patch. If anyone has any objections, please let me know.
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From: Eric Dumazet <edumazet@google.com>
[ Upstream commit 2359a47671fc4fb0fe5e9945f76c2cb10792c0f8 ]
One condition before codel_Newton_step() was not good if we never left the dropping state for a flow. As a result rec_inv_sqrt was 0, instead of the ~0 initial value.
codel control law was then set to a very aggressive mode, dropping many packets before reaching 'target' and recovering from this problem.
To keep codel_vars_init() as efficient as possible, refine the condition to make sure rec_inv_sqrt initial value is correct
Many thanks to Anton Mich for discovering the issue and suggesting a fix.
Reported-by: Anton Mich <lp2s1h@gmail.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> --- include/net/codel.h | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
--- a/include/net/codel.h +++ b/include/net/codel.h @@ -305,6 +305,8 @@ static struct sk_buff *codel_dequeue(str } } } else if (drop) { + u32 delta; + if (params->ecn && INET_ECN_set_ce(skb)) { stats->ecn_mark++; } else { @@ -320,9 +322,11 @@ static struct sk_buff *codel_dequeue(str * assume that the drop rate that controlled the queue on the * last cycle is a good starting point to control it now. */ - if (codel_time_before(now - vars->drop_next, + delta = vars->count - vars->lastcount; + if (delta > 1 && + codel_time_before(now - vars->drop_next, 16 * params->interval)) { - vars->count = (vars->count - vars->lastcount) | 1; + vars->count = delta; /* we dont care if rec_inv_sqrt approximation * is not very precise : * Next Newton steps will correct it quadratically.
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