Bug #359

Fwd: [PATCH] tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample

Added by David Taht about 1 year ago. Updated about 1 year ago.

Status:Closed Start date:
Priority:Normal Due date:
Assignee:Dave Täht % Done:

0%
Category:Linux Kernel Spent time: 0.50 hour
Target version:1st Public Cerowrt release

Description

---------- Forwarded message ----------
From: David Miller <>
Date: Tue, Apr 10, 2012 at 11:47 AM
Subject: Re: [PATCH] tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample
To:
Cc: , , ,
,

From: Neal Cardwell <>
Date: Tue, 10 Apr 2012 13:59:20 -0400

Fix a code path in tcp_rcv_rtt_update() that was comparing scaled and unscaled RTT samples.

The intent in the code was to only use the 'm' measurement if it was a new minimum.  However, since 'm' had not yet been shifted left 3 bits but 'new_sample' had, this comparison would nearly always succeed, leading us to erroneously set our receive-side RTT estimate to the 'm' sample when that sample could be nearly 8x too high to use.

The overall effect is to often cause the receive-side RTT estimate to be significantly too large (up to 40% too large for brief periods in my tests).

Signed-off-by: Neal Cardwell <>

Applied, thanks.

History

#1
Updated by Dave Täht about 1 year ago

  • Target version set to 1st Public Cerowrt release
  • Assignee set to Dave Täht
  • Status changed from New to Closed
  • Category set to Linux Kernel

Tested in cerowrt 3.3.2-6. Will probably be fixed in 3.3.3

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