Re: [PATCH net v5 3/5] net: macb: move ring size computation to functions

Hello Vineeth,

On Thu Sep 11, 2025 at 8:43 AM CEST, Karumanchi, Vineeth wrote:

On 9/10/2025 9:45 PM, Théo Lebrun wrote:

quoted

  #define DEFAULT_TX_RING_SIZE	512 /* must be power of 2 */
  #define MIN_TX_RING_SIZE	64
  #define MAX_TX_RING_SIZE	4096
-#define TX_RING_BYTES(bp) (macb_dma_desc_get_size(bp) \
- * (bp)->tx_ring_size)
  
  /* level of occupied TX descriptors under which we wake up TX process */
  #define MACB_TX_WAKEUP_THRESH(bp)	(3 * (bp)->tx_ring_size / 4)

@@ -2470,11 +2466,20 @@ static void macb_free_rx_buffers(struct macb *bp)
  	}
  }
  
+static unsigned int macb_tx_ring_size_per_queue(struct macb *bp)
+{
+ return macb_dma_desc_get_size(bp) * bp->tx_ring_size + bp- 
 >tx_bd_rd_prefetch;
+}
+
+static unsigned int macb_rx_ring_size_per_queue(struct macb *bp)
+{
+ return macb_dma_desc_get_size(bp) * bp->rx_ring_size + bp- 
 >rx_bd_rd_prefetch;
+}
+

it would be good to have these functions as inline.
May be as a separate patch.

I don't see why? Compilers are clever pieces, they'll know to inline it.

If we added inline to macb_{tx,rx}_ring_size_per_queue(), should we also
add it to macb_dma_desc_get_size()? I do not know, but my compiler
decided to inline it as well. It might make other decisions on other
platforms.

Last point I see: those two functions are not called in the hotpath,
only at alloc & free. If we talk about inline for the theoretical speed
gain, then it doesn't matter in that case. If it is a code size aspect,
then once again the compiler is more aware than myself.

I don't like the tone, but it is part of the kernel doc and is on topic:
https://www.kernel.org/doc/html/latest/process/coding-style.html#the-inline-disease

Thanks Vineeth!

--
Théo Lebrun, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com