On Tue, Dec 13, 2022 at 01:22:40PM +0100, Christophe Leroy wrote:
From: Eric Dumazet edumazet@google.com
[ Upstream commit 62c07983bef9d3e78e71189441e1a470f0d1e653 ]
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-ErVB2jDdR... 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 Signed-off-by: Sasha Levin sashal@kernel.org Signed-off-by: Christophe Leroy christophe.leroy@csgroup.eu
include/linux/once.h | 28 ++++++++++++++++++++++++++++ lib/once.c | 30 ++++++++++++++++++++++++++++++ net/ipv4/inet_hashtables.c | 4 ++-- 3 files changed, 60 insertions(+), 2 deletions(-)
Now queued up, thanks.
greg k-h