[PATCH net] net: avoid an indirect call in ____sys_recvmsg()

[PATCH net] net: avoid an indirect call in ____sys_recvmsg()

[Eric Dumazet]

CONFIG_RETPOLINE=y made indirect calls expensive.

gcc seems to add an indirect call in ____sys_recvmsg().

Rewriting the code slightly makes sure to avoid this indirection.

Alternative would be to not call sock_recvmsg() and instead
use security_socket_recvmsg() and sock_recvmsg_nosec(),
but this is less readable IMO.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: David Laight <David.Laight@aculab.com>
---
 net/socket.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/net/socket.c b/net/socket.c
index ea28cbb9e2e7a7180ee63de2d09a81aacb001ab7..5af84d71cbc2f731def460b70aa7f68533a90b16 100644
--- a/net/socket.c
+++ b/net/socket.c
@@ -2559,7 +2559,12 @@ static int ____sys_recvmsg(struct socket *sock, struct msghdr *msg_sys,
 
 	if (sock->file->f_flags & O_NONBLOCK)
 		flags |= MSG_DONTWAIT;
-	err = (nosec ? sock_recvmsg_nosec : sock_recvmsg)(sock, msg_sys, flags);
+
+	if (unlikely(nosec))
+		err = sock_recvmsg_nosec(sock, msg_sys, flags);
+	else
+		err = sock_recvmsg(sock, msg_sys, flags);
+
 	if (err < 0)
 		goto out;
 	len = err;
-- 
2.24.0.393.g34dc348eaf-goog

Re: [PATCH net] net: avoid an indirect call in ____sys_recvmsg()

[Paolo Abeni]

On Fri, 2019-12-06 at 09:38 -0800, Eric Dumazet wrote:
> CONFIG_RETPOLINE=y made indirect calls expensive.
> 
> gcc seems to add an indirect call in ____sys_recvmsg().
> 
> Rewriting the code slightly makes sure to avoid this indirection.
> 
> Alternative would be to not call sock_recvmsg() and instead
> use security_socket_recvmsg() and sock_recvmsg_nosec(),
> but this is less readable IMO.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>
> Cc: Paolo Abeni <pabeni@redhat.com>
> Cc: David Laight <David.Laight@aculab.com>

I'm not sure this is -net material, but the code LGTM.

Acked-by: Paolo Abeni <pabeni@redhat.com>

Re: [PATCH net] net: avoid an indirect call in ____sys_recvmsg()

[Eric Dumazet]

On Fri, Dec 6, 2019 at 10:22 AM Paolo Abeni <pabeni@redhat.com> wrote:
>
>
> I'm not sure this is -net material, but the code LGTM.

Well, performance matters (otherwise David Laight would not have
investigated so much),
and patch is kind-of-trivial, I am pretty sure David Miller will not mind.

>
> Acked-by: Paolo Abeni <pabeni@redhat.com>

Thanks.

Re: [PATCH net] net: avoid an indirect call in ____sys_recvmsg()

[David Miller]

From: Eric Dumazet <edumazet@google.com>
Date: Fri,  6 Dec 2019 09:38:36 -0800

> CONFIG_RETPOLINE=y made indirect calls expensive.
> 
> gcc seems to add an indirect call in ____sys_recvmsg().
> 
> Rewriting the code slightly makes sure to avoid this indirection.
> 
> Alternative would be to not call sock_recvmsg() and instead
> use security_socket_recvmsg() and sock_recvmsg_nosec(),
> but this is less readable IMO.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks Eric.