Re: [PATCH V2 net-next 1/3] tcp: introduce TCP experimental option for SMC
From: David Miller <davem@davemloft.net>
Date: 2015-07-16 04:28:38
Also in:
linux-s390
From: Ursula Braun <redacted> Date: Tue, 14 Jul 2015 14:42:33 +0200
quoted hunk ↗ jump to hunk
diff --git a/include/linux/tcp.h b/include/linux/tcp.h index 48c3696..1b9a698 100644 --- a/include/linux/tcp.h +++ b/include/linux/tcp.h@@ -90,15 +90,28 @@ struct tcp_options_received { sack_ok : 4, /* SACK seen on SYN packet */ snd_wscale : 4, /* Window scaling received from sender */ rcv_wscale : 4; /* Window scaling to send to receiver */ + u8 smc_capability:1; /* SMC capability */ u8 num_sacks; /* Number of SACK blocks */ u16 user_mss; /* mss requested by user in ioctl */ u16 mss_clamp; /* Maximal mss, negotiated at connection setup */ };
This adds new space to this structure, which can be avoided. sack_ok only actually needs 3 bits, not 4, then you can use the extra bit for smc_capability.
quoted hunk ↗ jump to hunk
diff --git a/include/net/request_sock.h b/include/net/request_sock.h index 87935ca..dee47d2 100644 --- a/include/net/request_sock.h +++ b/include/net/request_sock.h@@ -55,7 +55,8 @@ struct request_sock { struct sock *rsk_listener; u16 mss; u8 num_retrans; /* number of retransmits */ - u8 cookie_ts:1; /* syncookie: encode tcpopts in timestamp */ + u8 cookie_ts:1, /* syncookie: encode tcpopts in timestamp */ + smc_capability:1; u8 num_timeout:7; /* number of timeouts */ /* The following two fields can be easily recomputed I think -AK */ u32 window_clamp; /* window clamp at creation time */
Again, similar situation here. Please find a way to add your new boolean value without expanding the size of this structure. Here is it clear that a single u8 is fully consumed by the cookie_ts and num_timeout bit fields.
+#if IS_ENABLED(CONFIG_AFSMC)
I think this ifdef is completely pointless. What do you think every Linux distribution is going to do for their kernels? They are going to turn everything on. So you need to find a way for your new feature to be nearly zero cost, especially in the fast paths, assuming the code is enabled.