netdev - Re: Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause to Troughput drop when enable NO_HZ_IDEL or HIGH_RES

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Date:	Tue, 6 May 2014 12:48:27 -0400
From:	Neal Cardwell <ncardwell@...gle.com>
To:	V JobNickname <workofv@...il.com>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: Is 3.18 patch "The tcp: TSO packets automatic sizing" will cause
 to Troughput drop when enable NO_HZ_IDEL or HIGH_RES_TIMERS ?

On Tue, May 6, 2014 at 12:17 PM, V JobNickname <workofv@...il.com> wrote:
> More detail trace, the first commit of 3.10.18, tcp: TSO packets
> automatic sizing, cause to this issue.
> https://git.kernel.org/cgit/linux/kernel/git/stable/linux-stable.git/diff/?id=5e25ba5003ee5de0ba2be56bfd54d16d4b1b028d

To provide another data point, it would be interesting to know what
performance you see with v3.15-rc4. Linux 3.15 has the following
patch:

 740b0f1841f6  tcp: switch rtt estimations to usec resolution

That patch switches tcp_update_pacing_rate() to use microsecond RTTs
for its calculation. That may help things in your case. (As Eric says,
more details would help.)

> I don't know why this TSO patch affect my network since the network
> driver doesn't enable NETIF_F_TSO.

Keep in mind that anytime the Linux TCP code or commit descriptions
talk about "TSO", the same applies to GSO. Is GSO enabled for your
device?

neal
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