netdev - RE: [PATCH v1 4/6] net: fec: Increase buffer descriptor entry number

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Message-ID: <e312c3c2120f4370bb9e9f5ab8a8c119@BLUPR03MB373.namprd03.prod.outlook.com>
Date:	Fri, 30 May 2014 15:46:49 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	David Laight <David.Laight@...LAB.COM>,
	"Frank.Li@...escale.com" <Frank.Li@...escale.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"shawn.guo@...aro.org" <shawn.guo@...aro.org>,
	"bhutchings@...arflare.com" <bhutchings@...arflare.com>,
	"stephen@...workplumber.org" <stephen@...workplumber.org>
Subject: RE: [PATCH v1 4/6] net: fec: Increase buffer descriptor entry number

From: Eric Dumazet <eric.dumazet@...il.com> Data: Friday, May 30, 2014 11:41 PM
>To: Duan Fugang-B38611
>Cc: ezequiel.garcia@...e-electrons.com; David Laight; Li Frank-B20596;
>davem@...emloft.net; netdev@...r.kernel.org; shawn.guo@...aro.org;
>bhutchings@...arflare.com; stephen@...workplumber.org
>Subject: RE: [PATCH v1 4/6] net: fec: Increase buffer descriptor entry
>number
>
>On Fri, 2014-05-30 at 15:08 +0000, fugang.duan@...escale.com wrote:
>
>> If frag page data is not match the alignment for ethernet DMA controller,
>there need three descriptor for one MSS:
>> One descriptor for headers, one for the first non-align bytes copied
>from frag page, one for the rest of frag page.
>>
>
>You could avoid the 2nd descriptor, by copying the unaligned part of the
>payload into first descriptor (containing headers : about 66 bytes or so
>you have room, if not, increase the 128 bytes room to 192 bytes)
>
>> So one frame may cost descriptor number is: 3 x 45
>
>May... but in general it would be closer of 2 * 45
>
Good idea!

>
>>
>> So the descriptors slots set to 512 is not big, just is reasonable. Do
>you think ?
>
>I believe it is fine : that is about 5 64KB TSO packets.
>

Thanks,
Andy