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

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Date:	Fri, 30 May 2014 09:42:34 +0000
From:	"fugang.duan@...escale.com" <fugang.duan@...escale.com>
To:	David Laight <David.Laight@...LAB.COM>,
	"Frank.Li@...escale.com" <Frank.Li@...escale.com>,
	"davem@...emloft.net" <davem@...emloft.net>
CC:	"ezequiel.garcia@...e-electrons.com" 
	<ezequiel.garcia@...e-electrons.com>,
	"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: David Laight <David.Laight@...LAB.COM> Data: Friday, May 30, 2014 5:11 PM
>To: Duan Fugang-B38611; Li Frank-B20596; davem@...emloft.net
>Cc: ezequiel.garcia@...e-electrons.com; 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
>
>From: Fugang Duan
>> In order to support SG, software TSO, let's increase BD entry number.
>
>Software TSO shouldn't significantly increase the number of descriptors
>required.
>I'd guess it makes a lot of packets have 2 fragments.
>
>...
>> -#define FEC_ENET_RX_PAGES	8
>> +#define FEC_ENET_RX_PAGES	256
>
>Supporting TSO shouldn't need more RX descriptors.
>While 16 descriptors isn't that many, 512 is a lot.
>If PAGE_SIZE is greater than 4k it is a huge amount of memory.
>
Yes, 16 descriptors is little, increase BD entry size can improve the performance.
And I want to add the later patch to support interrupt coalescing, which need more BD descriptors.

>>  #define FEC_ENET_RX_FRSIZE	2048
>>  #define FEC_ENET_RX_FRPPG	(PAGE_SIZE / FEC_ENET_RX_FRSIZE)
>>  #define RX_RING_SIZE		(FEC_ENET_RX_FRPPG * FEC_ENET_RX_PAGES)
>>  #define FEC_ENET_TX_FRSIZE	2048
>>  #define FEC_ENET_TX_FRPPG	(PAGE_SIZE / FEC_ENET_TX_FRSIZE)
>> -#define TX_RING_SIZE		16	/* Must be power of two */
>> -#define TX_RING_MOD_MASK	15	/*   for this to work */
>> +#define TX_RING_SIZE		512	/* Must be power of two */
>> +#define TX_RING_MOD_MASK	511	/*   for this to work */
>
>Does the driver support BQL (or similar) in order to limit the amount of
>queued tx traffic?
>Otherwise you've significantly increased the latency for connections other
>than one doing bulk tx.
>
>	David
>
The driver still don't support BQL.
I will add the feature to support FEC. Thanks for your advise.

Thanks,
Andy
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