By profiling, discovered that ena device driver allocates skb by
build_skb() and frees by napi_skb_cache_put(). Because the driver
does not use napi skb cache in allocation path, napi skb cache is
periodically filled and flushed. This is waste of napi skb cache.

As ena_alloc_skb() is called only in napi, Use napi_build_skb()
and napi_alloc_skb() when allocating skb.

This patch was tested on aws a1.metal instance.

[ jwiedmann.dev@gmail.com: Use napi_alloc_skb() instead of
  netdev_alloc_skb_ip_align() to keep things consistent. ]

Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Acked-by: Shay Agroskin <shayagr@amazon.com>
---
 drivers/net/ethernet/amazon/ena/ena_netdev.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c
index 53080fd143dc..07444aead3fd 100644
--- a/drivers/net/ethernet/amazon/ena/ena_netdev.c
+++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c
@@ -1400,10 +1400,9 @@ static struct sk_buff *ena_alloc_skb(struct ena_ring *rx_ring, void *first_frag)
 	struct sk_buff *skb;
 
 	if (!first_frag)
-		skb = netdev_alloc_skb_ip_align(rx_ring->netdev,
-						rx_ring->rx_copybreak);
+		skb = napi_alloc_skb(rx_ring->napi, rx_ring->rx_copybreak);
 	else
-		skb = build_skb(first_frag, ENA_PAGE_SIZE);
+		skb = napi_build_skb(first_frag, ENA_PAGE_SIZE);
 
 	if (unlikely(!skb)) {
 		ena_increase_stat(&rx_ring->rx_stats.skb_alloc_fail, 1,
-- 
2.33.1

Hello:

This patch was applied to netdev/net-next.git (master)
by Jakub Kicinski <kuba@kernel.org>:

On Sat, 29 Jan 2022 08:53:36 +0000 you wrote:
> By profiling, discovered that ena device driver allocates skb by
> build_skb() and frees by napi_skb_cache_put(). Because the driver
> does not use napi skb cache in allocation path, napi skb cache is
> periodically filled and flushed. This is waste of napi skb cache.
> 
> As ena_alloc_skb() is called only in napi, Use napi_build_skb()
> and napi_alloc_skb() when allocating skb.
> 
> [...]

Here is the summary with links:
  - [v2] net: ena: Do not waste napi skb cache
    https://git.kernel.org/netdev/net-next/c/7354a426e063

You are awesome, thank you!
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