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once: add DO_ONCE_SLOW() for sleepable contexts

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Christophe Leroy reported a ~80ms latency spike
happening at first TCP connect() time.

This is because __inet_hash_connect() uses get_random_once()
to populate a perturbation table which became quite big
after commit 4c2c8f03a5 ("tcp: increase source port perturb table to 2^16")

get_random_once() uses DO_ONCE(), which block hard irqs for the duration
of the operation.

This patch adds DO_ONCE_SLOW() which uses a mutex instead of a spinlock
for operations where we prefer to stay in process context.

Then __inet_hash_connect() can use get_random_slow_once()
to populate its perturbation table.

Fixes: 4c2c8f03a5 ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc82489 ("tcp: change source port randomizarion at connect() time")
Reported-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/netdev/CANn89iLAEYBaoYajy0Y9UmGFff5GPxDUoG-ErVB2jDdRNQ5Tug@mail.gmail.com/T/#t
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Willy Tarreau <w@1wt.eu>
Tested-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2022-10-01 13:51:02 -07:00 • committed by David S. Miller
parent f75886a045
commit 62c07983be
3 changed files with 60 additions and 2 deletions
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28
include/linux/once.h
View file

@ -5,10 +5,18 @@
#include <linux/types.h>
#include <linux/jump_label.h>
/* Helpers used from arbitrary contexts.
* Hard irqs are blocked, be cautious.
*/
bool __do_once_start(bool *done, unsigned long *flags);
void __do_once_done(bool *done, struct static_key_true *once_key,
unsigned long *flags, struct module *mod);
/* Variant for process contexts only. */
bool __do_once_slow_start(bool *done);
void __do_once_slow_done(bool *done, struct static_key_true *once_key,
struct module *mod);
/* Call a function exactly once. The idea of DO_ONCE() is to perform
* a function call such as initialization of random seeds, etc, only
* once, where DO_ONCE() can live in the fast-path. After @func has
@ -52,7 +60,27 @@ void __do_once_done(bool *done, struct static_key_true *once_key,
___ret; \
})
/* Variant of DO_ONCE() for process/sleepable contexts. */
#define DO_ONCE_SLOW(func, ...) \
({ \
bool ___ret = false; \
static bool __section(".data.once") ___done = false; \
static DEFINE_STATIC_KEY_TRUE(___once_key); \
if (static_branch_unlikely(&___once_key)) { \
___ret = __do_once_slow_start(&___done); \
if (unlikely(___ret)) { \
func(__VA_ARGS__); \
__do_once_slow_done(&___done, &___once_key, \
THIS_MODULE); \
} \
} \
___ret; \
})
#define get_random_once(buf, nbytes) \
DO_ONCE(get_random_bytes, (buf), (nbytes))
#define get_random_slow_once(buf, nbytes) \
DO_ONCE_SLOW(get_random_bytes, (buf), (nbytes))
#endif /* _LINUX_ONCE_H */