[PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

[PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

[Eric Dumazet]

trafgen performance considerably sank on hosts with many cores
after the blamed commit.

packet_read_pending() is very expensive, and calling it
in af_packet fast path defeats Daniel intent in commit
b013840810c2 ("packet: use percpu mmap tx frame pending refcount")

tpacket_destruct_skb() makes room for one packet, we can immediately
wakeup a producer, no need to completely drain the tx ring.

Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Neil Horman <nhorman@tuxdriver.com>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>
---
 net/packet/af_packet.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index 8c6d3fbb4ed87f17c2e365810106a05fe9b8ff0c..ea3ebc160e25cc661901717a755f47db927c304d 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -2522,8 +2522,7 @@ static void tpacket_destruct_skb(struct sk_buff *skb)
 		ts = __packet_set_timestamp(po, ph, skb);
 		__packet_set_status(po, ph, TP_STATUS_AVAILABLE | ts);
 
-		if (!packet_read_pending(&po->tx_ring))
-			complete(&po->skb_completion);
+		complete(&po->skb_completion);
 	}
 
 	sock_wfree(skb);
-- 
2.45.0.rc1.225.g2a3ae87e7f-goog

Re: [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

[Willem de Bruijn]

Eric Dumazet wrote:
> trafgen performance considerably sank on hosts with many cores
> after the blamed commit.
> 
> packet_read_pending() is very expensive, and calling it
> in af_packet fast path defeats Daniel intent in commit
> b013840810c2 ("packet: use percpu mmap tx frame pending refcount")
> 
> tpacket_destruct_skb() makes room for one packet, we can immediately
> wakeup a producer, no need to completely drain the tx ring.
> 
> Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

Thanks!

Re: [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

[patchwork-bot+netdevbpf]

Hello:

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

On Wed, 15 May 2024 16:33:58 +0000 you wrote:
> trafgen performance considerably sank on hosts with many cores
> after the blamed commit.
> 
> packet_read_pending() is very expensive, and calling it
> in af_packet fast path defeats Daniel intent in commit
> b013840810c2 ("packet: use percpu mmap tx frame pending refcount")
> 
> [...]

Here is the summary with links:
  - [net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()
    https://git.kernel.org/netdev/net/c/581073f626e3

You are awesome, thank you!
-- 
Deet-doot-dot, I am a bot.
https://korg.docs.kernel.org/patchwork/pwbot.html

Re: [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct_skb()

[Daniel Borkmann]

On 5/15/24 6:33 PM, Eric Dumazet wrote:
> trafgen performance considerably sank on hosts with many cores
> after the blamed commit.
> 
> packet_read_pending() is very expensive, and calling it
> in af_packet fast path defeats Daniel intent in commit
> b013840810c2 ("packet: use percpu mmap tx frame pending refcount")
> 
> tpacket_destruct_skb() makes room for one packet, we can immediately
> wakeup a producer, no need to completely drain the tx ring.
> 
> Fixes: 89ed5b519004 ("af_packet: Block execution of tasks waiting for transmit to complete in AF_PACKET")
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: Daniel Borkmann <daniel@iogearbox.net>
> Cc: Willem de Bruijn <willemdebruijn.kernel@gmail.com>

Acked-by: Daniel Borkmann <daniel@iogearbox.net>

Thanks Eric!