This is a note to let you know that I've just added the patch titled
bgmac: reduce max frame size to support just MTU 1500
to the 5.15-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
bgmac-reduce-max-frame-size-to-support-just-mtu-1500.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 055773b1dfdb05a2165b9bcc8d88ed6611c028a5
Author: Rafał Miłecki <rafal@xxxxxxxxxx>
Date: Mon Jan 27 09:51:59 2025 -0800
bgmac: reduce max frame size to support just MTU 1500
[ Upstream commit 752e5fcc2e77358936d36ef8e522d6439372e201 ]
bgmac allocates new replacement buffer before handling each received
frame. Allocating & DMA-preparing 9724 B each time consumes a lot of CPU
time. Ideally bgmac should just respect currently set MTU but it isn't
the case right now. For now just revert back to the old limited frame
size.
This change bumps NAT masquerade speed by ~95%.
Since commit 8218f62c9c9b ("mm: page_frag: use initial zero offset for
page_frag_alloc_align()"), the bgmac driver fails to open its network
interface successfully and runs out of memory in the following call
stack:
bgmac_open
-> bgmac_dma_init
-> bgmac_dma_rx_skb_for_slot
-> netdev_alloc_frag
BGMAC_RX_ALLOC_SIZE = 10048 and PAGE_FRAG_CACHE_MAX_SIZE = 32768.
Eventually we land into __page_frag_alloc_align() with the following
parameters across multiple successive calls:
__page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=0
__page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=10048
__page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=20096
__page_frag_alloc_align: fragsz=10048, align_mask=-1, size=32768, offset=30144
So in that case we do indeed have offset + fragsz (40192) > size (32768)
and so we would eventually return NULL. Reverting to the older 1500
bytes MTU allows the network driver to be usable again.
Fixes: 8c7da63978f1 ("bgmac: configure MTU and add support for frames beyond 8192 byte size")
Signed-off-by: Rafał Miłecki <rafal@xxxxxxxxxx>
[florian: expand commit message about recent commits]
Reviewed-by: Simon Horman <horms@xxxxxxxxxx>
Signed-off-by: Florian Fainelli <florian.fainelli@xxxxxxxxxxxx>
Link: https://patch.msgid.link/20250127175159.1788246-1-florian.fainelli@xxxxxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/drivers/net/ethernet/broadcom/bgmac.h b/drivers/net/ethernet/broadcom/bgmac.h
index 99a344175a751..378c72bfbd9e5 100644
--- a/drivers/net/ethernet/broadcom/bgmac.h
+++ b/drivers/net/ethernet/broadcom/bgmac.h
@@ -328,8 +328,7 @@
#define BGMAC_RX_FRAME_OFFSET 30 /* There are 2 unused bytes between header and real data */
#define BGMAC_RX_BUF_OFFSET (NET_SKB_PAD + NET_IP_ALIGN - \
BGMAC_RX_FRAME_OFFSET)
-/* Jumbo frame size with FCS */
-#define BGMAC_RX_MAX_FRAME_SIZE 9724
+#define BGMAC_RX_MAX_FRAME_SIZE 1536
#define BGMAC_RX_BUF_SIZE (BGMAC_RX_FRAME_OFFSET + BGMAC_RX_MAX_FRAME_SIZE)
#define BGMAC_RX_ALLOC_SIZE (SKB_DATA_ALIGN(BGMAC_RX_BUF_SIZE + BGMAC_RX_BUF_OFFSET) + \
SKB_DATA_ALIGN(sizeof(struct skb_shared_info)))
