netdev - Re: [PATCH net-next] tcp: cache RTAX_QUICKACK metric in a hot cache line

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Message-ID: <20250317195741.21337-1-kuniyu@amazon.com>
Date: Mon, 17 Mar 2025 12:57:28 -0700
From: Kuniyuki Iwashima <kuniyu@...zon.com>
To: <edumazet@...gle.com>
CC: <davem@...emloft.net>, <eric.dumazet@...il.com>, <horms@...nel.org>,
	<kuba@...nel.org>, <kuniyu@...zon.com>, <ncardwell@...gle.com>,
	<netdev@...r.kernel.org>, <pabeni@...hat.com>
Subject: Re: [PATCH net-next] tcp: cache RTAX_QUICKACK metric in a hot cache line

From: Eric Dumazet <edumazet@...gle.com>
Date: Wed, 12 Mar 2025 08:39:07 +0000
> tcp_in_quickack_mode() is called from input path for small packets.
> 
> It calls __sk_dst_get() which reads sk->sk_dst_cache which has been
> put in sock_read_tx group (for good reasons).
> 
> Then dst_metric(dst, RTAX_QUICKACK) also needs extra cache line misses.
> 
> Cache RTAX_QUICKACK in icsk->icsk_ack.dst_quick_ack to no longer pull
> these cache lines for the cases a delayed ACK is scheduled.
> 
> After this patch TCP receive path does not longer access sock_read_tx
> group.
> 
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...zon.com>