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From: Ben Hutchings <bhutchings@solarflare.com>
To: Eric Dumazet <eric.dumazet@gmail.com>
Cc: "Grant Grundler" <grundler@google.com>,
	"Freddy Xin" <freddy@asix.com.tw>,
	"David Miller" <davem@davemloft.net>,
	netdev <netdev@vger.kernel.org>,
	linux-usb@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
	"ASIX Louis [蘇威陸]" <louis@asix.com.tw>,
	"Allan Chou" <allan@asix.com.tw>
Subject: Re: [PATCH 1/1] TX throttling bug-fixing patch of AX88179_178A
Date: Mon, 22 Jul 2013 20:47:51 +0100	[thread overview]
Message-ID: <1374522471.1635.48.camel@bwh-desktop.uk.level5networks.com> (raw)
In-Reply-To: <1374518841.4990.26.camel@edumazet-glaptop>

On Mon, 2013-07-22 at 11:47 -0700, Eric Dumazet wrote:
> On Mon, 2013-07-22 at 19:38 +0100, Ben Hutchings wrote:
> > On Mon, 2013-07-22 at 11:29 -0700, Grant Grundler wrote:
> > > On Mon, Jul 22, 2013 at 10:07 AM, Eric Dumazet <eric.dumazet@gmail.com> wrote:
> > > ...
> > > > I guess that if a driver does not advertise NETIF_F_SG, this
> > > > skb_linearize() call is not needed : All frames reaching your xmit
> > > > function should already be linear
> > > 
> > > As Ben Hutchings pointed out, hw_features is still setting this...but
> > > I'm not sure how that matters.
> > > 
> > > ax88179_set_features() doesn't allow setting SG or TSO features.  But
> > > I expect it would be "not too difficult" to add such that ethtool
> > > could set those features after boot.
> > [...]
> > 
> > It already can.  That's what putting feature flags in hw_features does.
> 
> My original concern, that inspired this patch, was to remove SG support,
> as this driver does not have SG support at all.
> 
> Linearize a full TSO packet needs order-5 allocations, thats likely to
> fail and lead to very slow TCP performance, because it will only rely on
> retransmits.

The driver could set gso_max_size to reduce that problem.  But I rather
doubt that TSO followed by skb_linearize() significantly improves
throughput or CPU-efficiency.  (If the device has a 1G link but is
connected to the host through a USB 2.0 port, then USB is the bottleneck
and TSO could improve throughput a few percent.  But that's a silly
configuration.)

The real solution would be for someone to add SG support to the usbnet
core.  Trying to support 1GbE with only linear skbs is not a great
idea... and it can only be a matter of time before there is USB ultra
speed (or whatever comes after 'super') with 10GbE devices...

Ben.

-- 
Ben Hutchings, Staff Engineer, Solarflare
Not speaking for my employer; that's the marketing department's job.
They asked us to note that Solarflare product names are trademarked.

  reply	other threads:[~2013-07-22 19:47 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-07-20  9:16 freddy
2013-07-22 17:07 ` Eric Dumazet
2013-07-22 17:11   ` Ben Hutchings
2013-07-22 18:29   ` Grant Grundler
2013-07-22 18:38     ` Ben Hutchings
2013-07-22 18:47       ` Eric Dumazet
2013-07-22 19:47         ` Ben Hutchings [this message]
     [not found]           ` <1374522471.1635.48.camel-/LGg1Z1CJKQ+9kgCwbf1HqK4ta4zdZpAajtMo4Cw6ucAvxtiuMwx3w@public.gmane.org>
2013-07-23  6:10             ` Eric Dumazet
2013-07-23 23:46               ` David Miller
2013-07-23 23:56                 ` Eric Dumazet
2013-07-24  0:05                   ` Eric Dumazet
2013-07-24  0:15                     ` [PATCH] usbnet: do not pretend to support SG/TSO Eric Dumazet
2013-07-26 20:48                       ` David Miller
2013-07-24  0:17                     ` [PATCH 1/1] TX throttling bug-fixing patch of AX88179_178A David Miller
2013-07-24  2:29                 ` Grant Grundler
     [not found]                   ` <CANEJEGtLavwdPdq_Qojz_x-DQ3KXfZp0vPYr6imKtNxN0Hf_2Q-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-07-24  2:32                     ` Grant Grundler
2013-07-25  2:28               ` Ming Lei
2013-07-25  5:10                 ` Eric Dumazet
2013-07-25  5:25                   ` Ming Lei
     [not found]                     ` <CACVXFVNyFk0Zpi4tC0ENiq8RcrtrjYW-Dhs+A56+Pw4BKm8y8A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-07-25 11:01                       ` Eric Dumazet
2013-07-25 14:52                         ` Ming Lei
2013-07-25 15:00                           ` Ben Hutchings
     [not found]                           ` <CACVXFVNre5SsJhaVqFNRcop7ahqxabWqHZkjBZccj1ZqOAUZ9A-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2013-07-25 15:11                             ` Eric Dumazet
2013-07-25 13:34                     ` Ben Hutchings

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