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authorEric Dumazet <edumazet@google.com>2014-03-19 21:02:21 -0700
committerDavid S. Miller <davem@davemloft.net>2014-03-20 16:22:42 -0400
commit632623153196bf183a69686ed9c07eee98ff1bf8 (patch)
tree1e09d6a821d8b176f08da6a4e3c24c63a2b2c4ea /include/net
parent88050049e7111f074e8887ba5a4cefc9f8fa8d41 (diff)
tcp: syncookies: do not use getnstimeofday()
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 get_jiffies_64(), as this is more than enough, and go back to 60 seconds periods. Fixes: 8c27bd75f04f ("tcp: syncookies: reduce cookie lifetime to 128 seconds") Signed-off-by: Eric Dumazet <edumazet@google.com> Cc: Florian Westphal <fw@strlen.de> Acked-by: Florian Westphal <fw@strlen.de> Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'include/net')
-rw-r--r--include/net/tcp.h11
1 files changed, 6 insertions, 5 deletions
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 8c4dd63134d4..743accec6c76 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -480,20 +480,21 @@ struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb,
#ifdef CONFIG_SYN_COOKIES
#include <linux/ktime.h>
-/* Syncookies use a monotonic timer which increments every 64 seconds.
+/* Syncookies use a monotonic timer which increments every 60 seconds.
* 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*60 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 */
+ u64 val = get_jiffies_64();
+
+ do_div(val, 60 * HZ);
+ return val;
}
u32 __cookie_v4_init_sequence(const struct iphdr *iph, const struct tcphdr *th,