From: "Ilpo Järvinen" <ilpo.jarvinen@helsinki.fi>
To: David Miller <davem@davemloft.net>
Cc: Yuchung Cheng <ycheng@google.com>,
ncardwell@google.com, Netdev <netdev@vger.kernel.org>,
edumazet@google.com
Subject: Re: [PATCH net 4/5] tcp: prevent bogus undos when SACK is not enabled
Date: Tue, 13 Mar 2018 12:24:50 +0200 (EET) [thread overview]
Message-ID: <alpine.DEB.2.20.1803131201160.29120@whs-18.cs.helsinki.fi> (raw)
In-Reply-To: <20180309.102357.98405985881146907.davem@davemloft.net>
[-- Attachment #1: Type: text/plain, Size: 1067 bytes --]
On Fri, 9 Mar 2018, David Miller wrote:
> From: Ilpo Jï¿œrvinen <ilpo.jarvinen@helsinki.fi>
> Date: Fri, 9 Mar 2018 16:11:47 +0200 (EET)
>
> > Unfortunately I don't have now permission to publish the time-seq
> > graph about it but I've tried to improve the changelog messages so
> > that you can better understand under which conditions the problem
> > occurs.
>
> It is indeed extremely unfortunate that you wish to justify a change
> for which you cannot provide the supporting data at all.
Here is the time-seqno graph about the issue:
https://www.cs.helsinki.fi/u/ijjarvin/linux/nonsackbugs/recovery_undo_bug.pdf
First the correct CC action (wnd reduction) occurs; then bogus undo
causes bursting back to the window with which the congestion losses
occurred earlier; because of the burst, some packets get lost due to
congestion again.
The sender is actually somewhat lucky here: If only one packet would get
lost instead of three, the same process would repeat for the next recovery
(as cumulative ACK to high_seq condition would reoccur).
--
i.
next prev parent reply other threads:[~2018-03-13 10:25 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-07 12:59 [PATCH net 0/5] tcp: fixes to non-SACK TCP Ilpo Järvinen
2018-03-07 12:59 ` [PATCH net 1/5] tcp: feed correct number of pkts acked to cc modules also in recovery Ilpo Järvinen
2018-03-07 12:59 ` [PATCH net 2/5] tcp: prevent bogus FRTO undos with non-SACK flows Ilpo Järvinen
2018-03-07 19:24 ` Neal Cardwell
2018-03-07 19:54 ` Yuchung Cheng
2018-03-07 22:19 ` Ilpo Järvinen
2018-03-07 12:59 ` [PATCH net 3/5] tcp: move false FR condition into tcp_false_fast_retrans_possible() Ilpo Järvinen
2018-03-07 15:50 ` Eric Dumazet
2018-03-07 12:59 ` [PATCH net 4/5] tcp: prevent bogus undos when SACK is not enabled Ilpo Järvinen
2018-03-07 20:19 ` Neal Cardwell
2018-03-07 23:48 ` Yuchung Cheng
2018-03-09 14:11 ` Ilpo Järvinen
2018-03-09 14:32 ` Eric Dumazet
2018-03-09 15:28 ` David Miller
2018-03-09 15:23 ` David Miller
2018-03-09 19:23 ` Ilpo Järvinen
2018-03-13 10:24 ` Ilpo Järvinen [this message]
2018-03-07 12:59 ` [PATCH net 5/5] tcp: send real dupACKs by locking advertized window for non-SACK flows Ilpo Järvinen
2018-03-07 15:58 ` Eric Dumazet
2018-03-07 20:09 ` Ilpo Järvinen
2018-03-07 20:13 ` Eric Dumazet
2018-03-07 21:39 ` Ilpo Järvinen
2018-03-07 22:01 ` Eric Dumazet
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