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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: 8c27bd75f0 ("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>
This commit is contained in:
Eric Dumazet 2014-03-19 21:02:21 -07:00 committed by David S. Miller
parent 88050049e7
commit 6326231531
1 changed files with 6 additions and 5 deletions
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11
include/net/tcp.h
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@ -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,