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.
next prev 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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