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From: David Miller <davem@davemloft.net>
To: ncardwell@google.com
Cc: netdev@vger.kernel.org, nanditad@google.com, ycheng@google.com,
	edumazet@google.com, therbert@google.com
Subject: Re: [PATCH] tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample
Date: Tue, 10 Apr 2012 14:47:37 -0400 (EDT)	[thread overview]
Message-ID: <20120410.144737.1047745906309843732.davem@davemloft.net> (raw)
In-Reply-To: <1334080760-968-1-git-send-email-ncardwell@google.com>

From: Neal Cardwell <ncardwell@google.com>
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 <ncardwell@google.com>

Applied, thanks.

  parent reply	other threads:[~2012-04-10 18:47 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-04-10 17:59 [PATCH] tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample Neal Cardwell
2012-04-10 18:45 ` Eric Dumazet
2012-04-10 18:47 ` David Miller [this message]
2012-04-10 20:46   ` Dave Taht
2012-04-10 21:07     ` David Miller
2012-04-10 21:11       ` Eric Dumazet
2012-04-10 21:16         ` David Miller
2012-04-10 21:22           ` Eric Dumazet
2012-04-10 21:24             ` Dave Taht

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