From: Dave Taht <dave.taht@gmail.com>
To: David Miller <davem@davemloft.net>
Cc: ncardwell@google.com, 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 13:46:38 -0700 [thread overview]
Message-ID: <CAA93jw5opbBobzkgJ2diRPu2X0aKOsnF9hmcm_LfsLPipeAK7g@mail.gmail.com> (raw)
In-Reply-To: <20120410.144737.1047745906309843732.davem@davemloft.net>
On Tue, Apr 10, 2012 at 11:47 AM, David Miller <davem@davemloft.net> wrote:
> 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.
> --
awesome, is this needed in stable?
--
Dave Täht
SKYPE: davetaht
US Tel: 1-239-829-5608
http://www.bufferbloat.net
next prev parent reply other threads:[~2012-04-10 20:46 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
2012-04-10 20:46 ` Dave Taht [this message]
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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