netdev - [PATCH net] net: use indirect calls helpers for sk_exit_memory

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Date:   Wed,  1 Mar 2023 13:32:47 +0000
From:   Eric Dumazet <edumazet@...gle.com>
To:     "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,
        Brian Vazquez <brianvv@...gle.com>,
        Florian Westphal <fw@...len.de>,
        Eric Dumazet <edumazet@...gle.com>
Subject: [PATCH net] net: use indirect calls helpers for sk_exit_memory_pressure()

From: Brian Vazquez <brianvv@...gle.com>

Florian reported a regression and sent a patch with the following
changelog:

<quote>
 There is a noticeable tcp performance regression (loopback or cross-netns),
 seen with iperf3 -Z (sendfile mode) when generic retpolines are needed.

 With SK_RECLAIM_THRESHOLD checks gone number of calls to enter/leave
 memory pressure happen much more often. For TCP indirect calls are
 used.

 We can't remove the if-set-return short-circuit check in
 tcp_enter_memory_pressure because there are callers other than
 sk_enter_memory_pressure.  Doing a check in the sk wrapper too
 reduces the indirect calls enough to recover some performance.

 Before,
 0.00-60.00  sec   322 GBytes  46.1 Gbits/sec                  receiver

 After:
 0.00-60.04  sec   359 GBytes  51.4 Gbits/sec                  receiver

 "iperf3 -c $peer -t 60 -Z -f g", connected via veth in another netns.
</quote>

It seems we forgot to upstream this indirect call mitigation we
had for years, lets do this instead.

[edumazet] - It seems we forgot to upstream this indirect call
             mitigation we had for years, let's do this instead.
           - Changed to INDIRECT_CALL_INET_1() to avoid bots reports.

Fixes: 4890b686f408 ("net: keep sk->sk_forward_alloc as small as possible")
Reported-by: Florian Westphal <fw@...len.de>
Link: https://lore.kernel.org/netdev/20230227152741.4a53634b@kernel.org/T/
Signed-off-by: Brian Vazquez <brianvv@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
---
 net/core/sock.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/net/core/sock.c b/net/core/sock.c
index 341c565dbc262fcece1c5b410609d910a68edcb0..c258887953905c340ad6deab8b66cbf45ecbf178 100644
--- a/net/core/sock.c
+++ b/net/core/sock.c
@@ -2818,7 +2818,8 @@ static void sk_enter_memory_pressure(struct sock *sk)
 static void sk_leave_memory_pressure(struct sock *sk)
 {
 	if (sk->sk_prot->leave_memory_pressure) {
-		sk->sk_prot->leave_memory_pressure(sk);
+		INDIRECT_CALL_INET_1(sk->sk_prot->leave_memory_pressure,
+				     tcp_leave_memory_pressure, sk);
 	} else {
 		unsigned long *memory_pressure = sk->sk_prot->memory_pressure;
 
-- 
2.40.0.rc0.216.gc4246ad0f0-goog