diff mbox

tcp: syncookies: do not use getnstimeofday()

Message ID 1395263181.9114.69.camel@edumazet-glaptop2.roam.corp.google.com
State Superseded, archived
Delegated to: David Miller
Headers show

Commit Message

Eric Dumazet March 19, 2014, 9:06 p.m. UTC 
From: Eric Dumazet <edumazet@google.com>

While it is true that getnstimeofday() uses about 40 cycles if TSC
is available, it can use 1600 cycles if hpet is the clocksource.

Switch to local_clock(). This one consumes 26 cycles and is not
impacted by a date/time change.

Fixes: 8c27bd75f04f ("tcp: syncookies: reduce cookie lifetime to 128 seconds")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Florian Westphal <fw@strlen.de>
---
 include/net/tcp.h |    7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)



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Comments

Florian Westphal March 19, 2014, 10:56 p.m. UTC | #1 
Eric Dumazet <eric.dumazet@gmail.com> wrote:
> While it is true that getnstimeofday() uses about 40 cycles if TSC
> is available, it can use 1600 cycles if hpet is the clocksource.

Ouch.  Why is secure_tcp_sequence_number also using
ktime_get_real/getnstimeofday?

clock drift when other cpu is used?

[ Just curious; I have no objections to this patch ]
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diff mbox

Patch

diff --git a/include/net/tcp.h b/include/net/tcp.h
index bb253b9b2f06..b7e524bb297e 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -484,16 +484,15 @@  struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
  * This counter is used both as a hash input and partially encoded into
  * the cookie value.  A cookie is only validated further if the delta
  * between the current counter value and the encoded one is less than this,
- * i.e. a sent cookie is valid only at most for 128 seconds (or less if
+ * i.e. a sent cookie is valid only at most for 2*68 seconds (or less if
  * the counter advances immediately after a cookie is generated).
  */
 #define MAX_SYNCOOKIE_AGE 2
 
 static inline u32 tcp_cookie_time(void)
 {
-	struct timespec now;
-	getnstimeofday(&now);
-	return now.tv_sec >> 6; /* 64 seconds granularity */
+	/* 2^36 nsec = ~68.7 sec */
+	return local_clock() >> 36;
 }
 
 u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,