netdev - Re: Throughput regression with `tcp: refine TSO autosizing`

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Date:	Thu, 05 Feb 2015 06:41:26 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Michal Kazior <michal.kazior@...to.com>
Cc:	Neal Cardwell <ncardwell@...gle.com>,
	linux-wireless <linux-wireless@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	eyalpe@....mellanox.co.il
Subject: Re: Throughput regression with `tcp: refine TSO autosizing`

On Thu, 2015-02-05 at 14:44 +0100, Michal Kazior wrote:

> Ok. I tried calling skb_orphan() right after I submit each Tx frame
> (similar to niu which does this in start_xmit):
> 
> --- a/drivers/net/wireless/ath/ath10k/htt_tx.c
> +++ b/drivers/net/wireless/ath/ath10k/htt_tx.c
> @@ -564,6 +564,8 @@ int ath10k_htt_tx(struct ath10k_htt *htt, struct
> sk_buff *msdu)
>         if (res)
>                 goto err_unmap_msdu;
> 
> +       skb_orphan(msdu);
> +
>         return 0;
> 
>  err_unmap_msdu:
> 
> 
> Now, with {net/master + ath10k GRO + the above} I get 620mbps on a
> single flow (even better then before). Wow.
> 
> Does this look ok/safe as a solution to you?

Not at all. This basically removes backpressure.

A single UDP socket can now blast packets regardless of SO_SNDBUF
limits.

This basically remove years of work trying to fix bufferbloat.

I still do not understand why increasing tcp_limit_output_bytes is not
working for you.




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