The Tail Loss Probe RFC specifies that the PTO value should be set to
max(2 * SRTT, 10ms), where SRTT is the smoothed round-trip time.
The PTO value is converted to jiffies, so the timer may expire
prematurely.
This is especially problematic on systems in which HZ <= 100, so work
around this by setting the timeout to at least 2 jiffies on such
systems.
The 10ms figure was originally selected based on tests performed with
the current implementation and HZ = 1000. Thus, leave the behavior on
systems with HZ > 100 unchanged.
Signed-off-by: Ido Yariv <idox.ya...@intel.com>
---
net/ipv4/tcp_output.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index 534e5fd..5321df8 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2208,6 +2208,9 @@ bool tcp_schedule_loss_probe(struct sock *sk)
timeout = max_t(u32, timeout,
(rtt + (rtt >> 1) + TCP_DELACK_MAX));
timeout = max_t(u32, timeout, msecs_to_jiffies(10));
+#if HZ <= 100
+ timeout = max_t(u32, timeout, 2);
+#endif
/* If RTO is shorter, just schedule TLP in its place. */
tlp_time_stamp = tcp_time_stamp + timeout;
--
2.1.0
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