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This completes the retransmission (automated repeat-request, ARQ)
logic, sending (delayed) ACK messages when needed.
On deallocation, flows will ACK try to retransmit any remaining
unacknowledged messages (unless the FRCTFLINGER flag is turned off;
this is on by default). Applications can safely shut down as soon as
everything is ACK'd (i.e. the current Delta-t run is done). The
activity timeout is now passed to the IPCP for it to sleep before
completing deallocation (and releasing the flow_id). That should be
moved to the IRMd in due time.
The timerwheel is revised to be multi-level to reduce memory
consumption. The resolution bumps by a factor of 1 << RXMQ_BUMP (16)
and each level has RXMQ_SLOTS (1 << 8) slots. The lowest level has a
resolution of (1 << RXMQ_RES) (20) ns, which is roughly a
millisecond. Currently, 3 levels are defined, so the largest delay we
can schedule at each level is:
Level 0: 256ms
Level 1: 4s
Level 2: about a minute.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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This adds the logic to send a pure acknowledgment packet without any
data to send. This needed the event filter for the fqueue, as these
non-data packets should not trigger application PKT events. The
default timeout is now 10ms, until we have FRCP tuning as part of
fccntl.
Karn's algorithm seems to be very unstable with low (sub-ms) RTT
estimates. Doubling RTO (every RTO) seems still too slow to prevent
rtx storms when the measured rtt suddenly spikes several orders of
magnitude. Just assuming the ACK'd packet is the last one transmitted
seems to be a lot more stable. It can lead to temporary
underestimation, but this is not a throughput-killer in FRCP.
Changes most time units to nanoseconds for faster computation.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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The retransmission was always disabling the DRF flag. This caused
problems with the loss of the first packet, which of course needs a
DRF flag set. The retransmitted packet will now contain a the original
DRF flag and an updated ack number.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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The single retransmission wheel caused locking headaches as the calls
for different flows could block on the same rxmwheel. This stabilizes
the stack, but if the rdrbuff gets full there can now be big delays.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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Fixes infinite rescheduling with RTO getting lower than the timerwheel
resolution. For very low RTO values we'd need a big packet buffer with
the current memory allocator implementation (rdrbuff). Setting a
(configurable) minimum RTO (250 us) reduces this need.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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There were a bunch of bugs in FRCP that urgently needed fixing. Now
data QoS is usable even with heavy packet loss (within some
parameters). The current RTT estimator is the IETF one. It should be
updated to the improved one used in the Linux kernel once the A-timer
(ACKs without data) and graceful shutdown are implemented.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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This adds a simple round-trip time estimator to FRCT. The estimate is
a weighted average with deviation. The retransmission is scheduled
after rtt + 2 times the deviation. A retransmit doubles the rtt
estimate to avoid the no-update case when rtt suddenly increases. The
rtt is estimated in microseconds and the granularity for retransmits
is 256 microseconds.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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Updates the copyright notice in all sources to 2019.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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The integrity check mechanism was split from FRCT, this flag is not
needed anymore.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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This fixes rudimentary automated repeat-request ARQ to correctly
configure the both connection records and use the receiver seqno. The
rto variable is moved out of the connection record.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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This adds rudimentary support for sending and processing
acknowledgments and doing retransmission.
It replaces the generic timerwheel with a specific one for
retransmission. This is currently a fixed wheel allowing
retransmissions to be scheduled up to about 32 seconds into the
future. It currently has an 8ms resolution. This could be made
configurable in the future. Failures of the flow (i.e. rtx not
working) are indicated by the rxmwheel_move() function returning a fd.
This is currently not yet handled (maybe just setting the state of the
flow to FLOWDOWN is a better solution).
The shm_rdrbuff tracks the number of users of a du_buff. One user is
the full stack, each retransmission will increment the refs counter
(which effectively acts as a semaphore). The refs counter is
decremented when a packet is acked. The du_buff is only allowed to be
removed if there is only one user left (the "stack").
When a packet is retransmitted, it is copied in the rdrbuff. This is
to ensure integrity of the packet when multiple layers do
retransmission and it is passed down the stack again.
Signed-off-by: Dimitri Staessens <[email protected]>
Signed-off-by: Sander Vrijders <[email protected]>
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