netdev - Re: linux-next network throughput performance regression

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Message-ID: <CALx6S34iGMPYF9AaHNNjtK03PXjTrW-Pxq6eFUwusoa=TbJsGQ@mail.gmail.com>
Date:	Sun, 8 Nov 2015 21:30:29 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Dexuan Cui <decui@...rosoft.com>
Cc:	David Miller <davem@...emloft.net>,
	"eric.dumazet@...il.com" <eric.dumazet@...il.com>,
	"dsa@...ulusnetworks.com" <dsa@...ulusnetworks.com>,
	Simon Xiao <sixiao@...rosoft.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devel@...uxdriverproject.org" <devel@...uxdriverproject.org>
Subject: Re: linux-next network throughput performance regression

On Sun, Nov 8, 2015 at 7:31 PM, Dexuan Cui <decui@...rosoft.com> wrote:
>> From: David Miller [mailto:davem@...emloft.net]
>> Sent: Monday, November 9, 2015 11:24
>> ...
>> > Thanks, David!
>> > I understand 1 TX queue is the bottleneck (however in Simon's
>> > test, TX=1 => 36.7Gb/s, TX=8 => 37.7 Gb/s, so it looks the TX=1 bottleneck
>> > is not so obvious).
>> > I'm just wondering how the bottleneck became much narrower with
>> > recent linux-next in Simon's result (36.7 Gb/s vs. 18.2 Gb/s). IMO there
>> > must be some latency somewhere.
>>
>> I think the whole thing here is that you misinterpreted what Eric said.
>>
>> He is not arguing that some regression did, or did not, happen.
>>
>> He instead was making the basic statement about the fact that due to
>> the lack of paralellness a single stream TCP case is harder to
>> optimize for high speed NICs.
>>
>> That is all.
> Thanks, I got it.
> I'm actually new to network performance tuning, trying to understand
> all the related details. :-)
>

You might want to look at
https://www.kernel.org/doc/Documentation/networking/scaling.txt as an
introduction to the scaling capabilities of the stack.

Tom

> Thanks,
> -- Dexuan
> --
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