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

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From: Eric Dumazet <eric.dumazet@xxxxxxxxx> Data: Friday, May 30, 2014 11:41 PM
>To: Duan Fugang-B38611
>Cc: ezequiel.garcia@xxxxxxxxxxxxxxxxxx; David Laight; Li Frank-B20596;
>davem@xxxxxxxxxxxxx; netdev@xxxxxxxxxxxxxxx; shawn.guo@xxxxxxxxxx;
>bhutchings@xxxxxxxxxxxxxx; stephen@xxxxxxxxxxxxxxxxxx
>Subject: RE: [PATCH v1 4/6] net: fec: Increase buffer descriptor entry
>number
>
>On Fri, 2014-05-30 at 15:08 +0000, fugang.duan@xxxxxxxxxxxxx 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
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