Can you do me a favour and give the attached patch a try, on your virtual
environment: this is a simpler solution.
I have tested it on loopback and found that some of the instabilities
disappear when clamping the RTT to a minimum value.
Fixing this is important even if it is "only" loopback: the problem will
re-appear on other high-speed interfaces.
[DCCP]: Ignory tiny RTTs
This lets DCCP ignore small RTT samples, by clamping all tiny values to
a minimum of 100 microseconds.
The impetus for this patch was instabilities which were observed in conjunction
with small RTTs in the CCID-3 module.
The chosen minimum of 100 microseconds is open to suggestion - it would be
possible to chose a higher value, on the other hand it seems not worth making
the single value a Kconfig option.
Signed-off-by: Gerrit Renker <gerrit@xxxxxxxxxxxxxx>
---
net/dccp/input.c | 5 +----
1 file changed, 1 insertion(+), 4 deletions(-)
--- a/net/dccp/input.c
+++ b/net/dccp/input.c
@@ -710,15 +710,12 @@ u32 dccp_sample_rtt(struct sock *sk, lon
/* dccpor_elapsed_time is either zeroed out or set and > 0 */
delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10;
- if (unlikely(delta <= 0)) {
- DCCP_WARN("unusable RTT sample %ld, using min\n", delta);
+ if (unlikely(delta < DCCP_SANE_RTT_MIN))
return DCCP_SANE_RTT_MIN;
- }
if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
DCCP_WARN("RTT sample %ld too large, using max\n", delta);
return DCCP_SANE_RTT_MAX;
}
-
return delta;
}
