netdev - Re: [PATCH net] af_packet: do not call packet_read_pending() from tpacket_destruct

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Date: Wed, 15 May 2024 14:02:59 -0400
From: Willem de Bruijn <willemdebruijn.kernel@...il.com>
To: Eric Dumazet <edumazet@...gle.com>, 
 "David S . Miller" <davem@...emloft.net>, 
 Jakub Kicinski <kuba@...nel.org>, 
 Paolo Abeni <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, 
 eric.dumazet@...il.com, 
 Eric Dumazet <edumazet@...gle.com>, 
 Neil Horman <nhorman@...driver.com>, 
 Daniel Borkmann <daniel@...earbox.net>, 
 Willem de Bruijn <willemdebruijn.kernel@...il.com>
Subject: Re: [PATCH net] af_packet: do not call packet_read_pending() from
 tpacket_destruct_skb()

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@...gle.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: Daniel Borkmann <daniel@...earbox.net>
> Cc: Willem de Bruijn <willemdebruijn.kernel@...il.com>

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

Thanks!