netdev - Re: [PATCH net-next] tcp: fix slow start after idle vs TSO/GSO

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Message-ID: <1440174431.6610.79.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Fri, 21 Aug 2015 09:27:11 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Neal Cardwell <ncardwell@...gle.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net-next] tcp: fix slow start after idle vs TSO/GSO

On Fri, 2015-08-21 at 11:10 -0400, Neal Cardwell wrote:

> Very nice catch, and this fix seems like a definite improvement.
> 
> One potential issue is that the connection can restart from idle not
> just because new data has been written (which this patch addresses),
> but also because the receive window opens and so now packets can be
> sent again. The old version of the code implicitly fired the restart
> code path in the "receive window opens" case as well, since it fired
> every time new data was sent. We might want to check if we need to
> call tcp_cwnd_restart() in tcp_ack_update_window(), next to the call
> for tcp_fast_path_check()?

Excellent, I wrote a 2nd packetdrill test to exercise this path, will
submit a v2 soon.

Thanks Neal


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