netdev - Re: linux-next network throughput performance regression

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Message-Id: <20151108.215247.1161049251544860672.davem@davemloft.net>
Date:	Sun, 08 Nov 2015 21:52:47 -0500 (EST)
From:	David Miller <davem@...emloft.net>
To:	decui@...rosoft.com
Cc:	eric.dumazet@...il.com, dsa@...ulusnetworks.com,
	sixiao@...rosoft.com, netdev@...r.kernel.org,
	haiyangz@...rosoft.com, linux-kernel@...r.kernel.org,
	devel@...uxdriverproject.org
Subject: Re: linux-next network throughput performance regression

From: Dexuan Cui <decui@...rosoft.com>
Date: Mon, 9 Nov 2015 02:39:24 +0000

>> Throughput on a single TCP flow for a 40G NIC can be tricky to tune.
> Why is a single TCP flow trickier than multiple TCP flows?
> IMO it should be easier to analyze the issue of a single TCP flow?

Because a single TCP flow can only use one of the many TX queues
that such modern NICs have.

The single TX queue becomes the bottleneck.

Whereas if you have several TCP flows, all of them can use independant
TX queues on the NIC in parallel to fill the link with traffic.

That's why.

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