From: David Laight <redacted> Data: Friday, May 30, 2014 5:11 PM

To: Duan Fugang-B38611; Li Frank-B20596; davem@davemloft.net
Cc: ezequiel.garcia@free-electrons.com; netdev@vger.kernel.org;
shawn.guo@linaro.org; bhutchings@solarflare.com;
stephen@networkplumber.org
Subject: RE: [PATCH v1 4/6] net: fec: Increase buffer descriptor entry
number

From: Fugang Duan

quoted

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.

...

quoted

-#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.

quoted

 #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