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| author | Eric Dumazet <edumazet@google.com> | 2022-10-01 13:51:02 -0700 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2022-10-03 13:29:11 +0100 |
| commit | 62c07983bef9d3e78e71189441e1a470f0d1e653 (patch) | |
| tree | f0ad523a6d93dcb8da22283a69298bbe16036083 /net/ipv4 | |
| parent | f75886a045531fedf4c11cf06d977a91f4cb266c (diff) | |
| download | lwn-62c07983bef9d3e78e71189441e1a470f0d1e653.tar.gz lwn-62c07983bef9d3e78e71189441e1a470f0d1e653.zip | |
once: add DO_ONCE_SLOW() for sleepable contexts
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 4c2c8f03a5ab ("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: 4c2c8f03a5ab ("tcp: increase source port perturb table to 2^16")
Fixes: 190cc82489f4 ("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>
Diffstat (limited to 'net/ipv4')
| -rw-r--r-- | net/ipv4/inet_hashtables.c | 4 |
1 files changed, 2 insertions, 2 deletions
diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 49db8c597eea..dc1c5629cd0d 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -958,8 +958,8 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, if (likely(remaining > 1)) remaining &= ~1U; - net_get_random_once(table_perturb, - INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb)); + get_random_slow_once(table_perturb, + INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb)); index = port_offset & (INET_TABLE_PERTURB_SIZE - 1); offset = READ_ONCE(table_perturb[index]) + (port_offset >> 32); |