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

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Date:	Thu, 05 Feb 2015 06:48:42 -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:

> I do get your point. But 1.5ms is really tough on Wi-Fi.
> 
> Just look at this:
> 
> ; ping 192.168.1.2 -c 3
> PING 192.168.1.2 (192.168.1.2) 56(84) bytes of data.
> 64 bytes from 192.168.1.2: icmp_seq=1 ttl=64 time=1.83 ms
> 64 bytes from 192.168.1.2: icmp_seq=2 ttl=64 time=2.02 ms
> 64 bytes from 192.168.1.2: icmp_seq=3 ttl=64 time=1.98 ms

Thats a different point.

I dont care about rtt but TX completions. (usually much much lower than
rtt)

I can have a 4 usec delay from the moment a NIC submits a packet to the
wire and I get TX completion IRQ, free the packet.

Yet the pong reply can come 100 ms later.

It does not mean the 4 usec delay is a problem.



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