netdev - Re: RE: [PATCH net-next 11/13] net: ethernet: aquantia: Refactoring buffers copying.

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Date:   Thu, 16 Feb 2017 17:02:28 +0100
From:   "Lino Sanfilippo" <LinoSanfilippo@....de>
To:     "David Laight" <David.Laight@...LAB.COM>
Cc:     "Pavel Belous" <Pavel.Belous@...antia.com>,
        "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "Simon Edelhaus" <Simon.Edelhaus@...antia.com>,
        "Alexey Andriyanov" <Alexey.Andriyanov@...antia.com>
Subject: Re: RE: [PATCH net-next 11/13] net: ethernet: aquantia: Refactoring
 buffers copying.

Hi,

> ...
> > Well, you should really try to avoid copying the tx buffers _at all_.
> > E.g. by passing self->buff_ring to aq_ring_tx_append_buffs() instead of
> > the temporary array.
> 
> Copying can help for horridly fragmented frames or when iommu (etc)
> setup is expensive.
> At least some ethernet hardware has minimum fragment lengths.
> 

I was referring to the copy of tx descriptors, not the frames/fragments itself. 
I wrote "tx buffers" because in this driver a descriptor is represented as
 a struct "aq_ring_buff_s". I cannot see a reason why this descriptor copy
 should be necessary.
However I agree that there can be circumstances that would justify even the
copy of frame/fragment data.

Regards,
Lino