Le 20/02/2022 à 08:53, Biju Das a écrit :
Hi Christophe,
Thanks for the patch.
Just a question, As per [1], former can be allocated from interrupt context.
But nothing mentioned for the allocation using the patch you mentioned[2]. I agree GFP_KERNEL
gives more opportunities of successful allocation.
Hi,
netdev_alloc_skb() uses an implicit GFP_ATOMIC, that is why it can be
safely called from an interrupt context.
__netdev_alloc_skb() is the same as netdev_alloc_skb(), except that you
can choose the GFP flag you want to use. ([1])
Here, the netdev_alloc_skb() is called just after some
"kcalloc(GFP_KERNEL);"
So this function can already NOT be called from interrupt context.
So if GFP_KERNEL is fine here for kcalloc(), it is fine also for
netdev_alloc_skb(), hence __netdev_alloc_skb(GFP_KERNEL).
Q1) Here it allocates 8K instead of 1K on each loop, Is there any limitation for netdev_alloc_skb for allocating 8K size?
Not sure to understand.
My patch does NOT change anything on the amount of memory allocated. it
only changes a GFP_ATOMIC into a GFP_KERNEL.
I'm not aware of specific limitation for netdev_alloc_skb().
My understanding is that in the worst case, it will behave just like
malloc() ([3])
So, if it was an issue before, it is still an issue after my patch.
Q2) In terms of allocation performance which is better netdev_alloc_skb or __netdev_alloc_skb?
AFAIK, there should be no difference, but __netdev_alloc_skb(GFP_KERNEL)
can succeed where netdev_alloc_skb() can fail. In such a case, it would
be slower but most importantly, it would succeed.
CJ
[1]:
https://elixir.bootlin.com/linux/v5.17-rc4/source/include/linux/skbuff.h#L2945
[2]:
https://elixir.bootlin.com/linux/v5.17-rc4/source/drivers/net/ethernet/renesas/ravb_main.c#L470
[3]:
https://elixir.bootlin.com/linux/v5.17-rc3/source/net/core/skbuff.c#L488
[1] https://www.kernel.org/doc/htmldocs/networking/API-netdev-alloc-skb.html
[2] https://www.kernel.org/doc/htmldocs/networking/API---netdev-alloc-skb.html
Regards,
Biju
Subject: [PATCH] ravb: Use GFP_KERNEL instead of GFP_ATOMIC when possible
'max_rx_len' can be up to GBETH_RX_BUFF_MAX (i.e. 8192) (see
'gbeth_hw_info').
The default value of 'num_rx_ring' can be BE_RX_RING_SIZE (i.e. 1024).
So this loop can allocate 8 Mo of memory.
Previous memory allocations in this function already use GFP_KERNEL, so
use __netdev_alloc_skb() and an explicit GFP_KERNEL instead of a implicit
GFP_ATOMIC.
This gives more opportunities of successful allocation.
Signed-off-by: Christophe JAILLET <christophe.jaillet@xxxxxxxxxx>
---
drivers/net/ethernet/renesas/ravb_main.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/net/ethernet/renesas/ravb_main.c
b/drivers/net/ethernet/renesas/ravb_main.c
index 24e2635c4c80..525d66f71f02 100644
--- a/drivers/net/ethernet/renesas/ravb_main.c
+++ b/drivers/net/ethernet/renesas/ravb_main.c
@@ -475,7 +475,7 @@ static int ravb_ring_init(struct net_device *ndev, int
q)
goto error;
for (i = 0; i < priv->num_rx_ring[q]; i++) {
- skb = netdev_alloc_skb(ndev, info->max_rx_len);
+ skb = __netdev_alloc_skb(ndev, info->max_rx_len, GFP_KERNEL);
if (!skb)
goto error;
ravb_set_buffer_align(skb);
--
2.32.0
