linux-kernel - Re: linux-next network throughput performance regression

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Date:	Sat, 07 Nov 2015 11:35:59 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Ahern <dsa@...ulusnetworks.com>
Cc:	Simon Xiao <sixiao@...rosoft.com>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	KY Srinivasan <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>
Subject: Re: linux-next network throughput performance regression

On Fri, 2015-11-06 at 14:30 -0700, David Ahern wrote:
> On 11/6/15 2:18 PM, Simon Xiao wrote:
> > The .config file used to build linux-next kernel is attached to this mail.
> 
> Thanks.
> 
> Failed to notice this on the first response; my brain filled in. Why 
> linux-next tree? Can you try net-next which is more relevant for this 
> mailing list, post the top commit id and config file used?

Throughput on a single TCP flow for a 40G NIC can be tricky to tune.

Make sure IRQ are properly setup/balanced, as I know that IRQ names were
changed recently and your scripts might have not noticed...

Also "ethtool -c eth0" might show very different interrupt coalescing
params ?

I too have a Mellanox 40Gb in my lab and saw no difference in
performance with recent kernels.

Of course, a simple "perf record -a -g sleep 4 ; perf report" might
point to some obvious issue. Like unexpected segmentation in case of
forwarding...

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