netdev - tcp: rearm RTO timer does not comply with RFC6298

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Date:   Wed, 20 Jan 2021 18:49:54 +0800
From:   Pengcheng Yang <yangpc@...gsu.com>
To:     ncardwell@...gle.com, ycheng@...gle.com
Cc:     netdev@...r.kernel.org, yangpc@...gsu.com
Subject: tcp: rearm RTO timer does not comply with RFC6298

hi,

I have a doubt about tcp_rearm_rto().

Early TCP always rearm the RTO timer to NOW+RTO when it receives
an ACK that acknowledges new data.

Referring to RFC6298 SECTION 5.3: "When an ACK is received that
acknowledges new data, restart the retransmission timer so that
it will expire after RTO seconds (for the current value of RTO)."

After ER and TLP, we rearm the RTO timer to *tstamp_of_head+RTO*
when switching from ER/TLP/RACK to original RTO in tcp_rearm_rto(),
in this case the RTO timer is triggered earlier than described in 
RFC6298, otherwise the same.

Is this planned? Or can we always rearm the RTO timer to 
tstamp_of_head+RTO?

Thanks.