2021-10-27 21:20:44

by Jason Xing

Subject: [PATCH net] net: gro: flush the real oldest skb

From: Jason Xing <[email protected]>

Prior to this patch, when the count of skbs of one flow is larger than
MAX_GRO_SKBS, gro_flush_oldest() flushes the tail of the list. However,
as we can see in the merge part of skb_gro_receive(), the tail of the
list is the newest, head oldest.

Here, we need to fetch the real oldest one and then process it to lower
the latency.

Fix: 07d78363dc ("net: Convert NAPI gro list into a small hash table.")
Signed-off-by: Jason Xing <[email protected]>
---
net/core/dev.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/dev.c b/net/core/dev.c
index 7ee9fec..d52ebdb 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -6012,7 +6012,7 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
{
struct sk_buff *oldest;

- oldest = list_last_entry(head, struct sk_buff, list);
+ oldest = list_first_entry(head, struct sk_buff, list);

/* We are called with head length >= MAX_GRO_SKBS, so this is
* impossible.
--
1.8.3.1

2021-10-27 21:26:34

by Jason Xing

Subject: Re: [PATCH net] net: gro: flush the real oldest skb

This patch has some problems. I got wrong with the @skb->list. Please ignore it.

Thanks,
Jason

On Wed, Oct 27, 2021 at 4:50 PM <[email protected]> wrote:
>
> From: Jason Xing <[email protected]>
>
> Prior to this patch, when the count of skbs of one flow is larger than
> MAX_GRO_SKBS, gro_flush_oldest() flushes the tail of the list. However,
> as we can see in the merge part of skb_gro_receive(), the tail of the
> list is the newest, head oldest.
>
> Here, we need to fetch the real oldest one and then process it to lower
> the latency.
>
> Fix: 07d78363dc ("net: Convert NAPI gro list into a small hash table.")
> Signed-off-by: Jason Xing <[email protected]>
> ---
> net/core/dev.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/net/core/dev.c b/net/core/dev.c
> index 7ee9fec..d52ebdb 100644
> --- a/net/core/dev.c
> +++ b/net/core/dev.c
> @@ -6012,7 +6012,7 @@ static void gro_flush_oldest(struct napi_struct *napi, struct list_head *head)
> {
> struct sk_buff *oldest;
>
> - oldest = list_last_entry(head, struct sk_buff, list);
> + oldest = list_first_entry(head, struct sk_buff, list);
>
> /* We are called with head length >= MAX_GRO_SKBS, so this is
> * impossible.
> --
> 1.8.3.1
>