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Date: Fri, 6 Feb 2015 15:09:36 +0100
Message-ID: <CA+BoTQkazCOin7VWLfrHUjtgKDPV6T+sFsk5FPS7D-morr4FZQ@mail.gmail.com> (sfid-20150206_150942_905009_DA3F73A3)
Subject: Re: Throughput regression with `tcp: refine TSO autosizing`
From: Michal Kazior <michal.kazior@tieto.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: Neal Cardwell <ncardwell@google.com>,
	linux-wireless <linux-wireless@vger.kernel.org>,
	Network Development <netdev@vger.kernel.org>,
	Eyal Perry <eyalpe@dev.mellanox.co.il>
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On 6 February 2015 at 14:53, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> On Fri, 2015-02-06 at 05:40 -0800, Eric Dumazet wrote:
>
>> tcp_wfree() could maintain in tp->tx_completion_delay_ms an EWMA
>> of TX completion delay. But this would require yet another expensive
>> call to ktime_get() if HZ < 1000.
>>
>> Then tcp_write_xmit() could use it to adjust :
>>
>>    limit = max(2 * skb->truesize, sk->sk_pacing_rate >> 9);
>>
>> to
>>
>>    amount = (2 + tp->tx_completion_delay_ms) * sk->sk_pacing_rate
>>
>>    limit = max(2 * skb->truesize, amount / 1000);
>>
>> I'll cook a patch.
>
> Hmm... doing this in all protocols would be too expensive,
> and we do not want to include time spent in qdiscs.
>
> wifi could eventually do that, providing in skb->tx_completion_delay_us
> the time spent in wifi driver.
>
> This way, we would have no penalty for network devices doing normal skb
> orphaning (loopback interface, ethernet, ...)

I'll play around with this idea and report back later.


Michał