Bug #359
Fwd: [PATCH] tcp: fix tcp_rcv_rtt_update() use of an unscaled RTT sample
Description
———- Forwarded message ———-From: David Miller davem@davemloft.net
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: ncardwell@google.com
Cc: netdev@vger.kernel.org, nanditad@google.com, ycheng@google.com,
edumazet@google.com, therbert@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.
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