Messages in this thread Patch in this message | | | From | Ido Yariv <> | Subject | [PATCH] net: tcp: Fix a PTO timing granularity issue | Date | Tue, 26 May 2015 16:17:17 -0400 |
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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.yariv@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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