| Commit message (Collapse) | Author | Age | Files | Lines |
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acknowledged
A link starts at 1,200 bytes; once an RTT is known it sends a PING padded
to 1,452 (DPLPMTUD, RFC 8899), alone and with the don't-fragment bit,
and uses that size once it is acknowledged. A probe lost is no
congestion; it is tried again a second on, three times, then ten minutes
on. GSO is asked for each burst (a control message), not the socket, so
a packet sent alone is never cut. CUBIC counts in the datagram.
On loopback packets fall by 19-27%; the CPU a record falls 13% at 1 KiB
and 7% at 16 KiB; in the simulator of a 50 Mbit/s path with 1% loss the
goodput rises from 6.1 to 7.0 Mbit/s (5%: 2.3 to 3.0).
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tbf with netem under it lost tbf's queue (netem became it), and the
answers queued behind the data. Now each way has its netem, the way to
the receivers' ports then a tbf whose queue holds a round trip; the way
back does not queue. transport.c takes its listener's port
(TRANSPORT_PORT).
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From the one after the last heard, letting be the ones heard before and
stopping at a gap: the listener's first delivery may begin past it when
packets reorder, which the harness counted as wrong.
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020-lossy-paths/run.py runs each case in an unprivileged namespace: a
50 Mbit/s tbf bottleneck under netem's delay, jitter and loss, both
ways. A link may send without UDP GSO (pure_link_gso), as netem takes a
burst as one packet; quinn the same (QUIC_GSO=0). transport.c and the
quinn harness give the records handed over in each 100 ms, and at a
steady rate the time each took; TCP CUBIC flows run beside them.
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links.c was a second implementation of the packet format; each device is
now a PureLinkSender on a socket of its own, keyed with a secret made
outside (pure_link_sender_shared: a key kept elsewhere, or a test's
many). M1 (1k, 10k) and M2 (10k, kill -9) pass with it: no silent step,
caught up in 0.2 s, every order applied once; the slowest store after
the restart is now the sender's 1 s wait for a word of the save
(STORED_WAIT), where the old devices tried again after 200 ms.
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link/link-protocol.h is the protocol with no socket, thread or clock of
its own: packets and time in, packets out. link/link.h carries it over
UDP as before. A sender starts small (8 flights, 16 records, a 4 KiB
ring) so one thread can hold many. The transport's CPU a record is the
same within 2% (five rounds each way, 61 B to 16 KiB).
test-link runs both sides through a network of its own: loss, packets
held back and doubled, failed saves, an idle sweep, and both sides
starting again, every record applied once as sent.
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A sender takes its messages' shape, and a listener asks its host which
input a stream goes to. The core gives the shape (pure_module_shape);
link/ now builds without the core's headers.
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libpure-link.a holds them; pure-serve and the M5 harness link it instead
of naming its source files.
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Between two pure-serve nodes, 16 KiB records drain at 33,600 a second
(23,000 before), the links spending 58 us a record (76), under quinn's 60
while the receiver also stores each one. 1,013 bytes: 406,000 a second
(347,000). Saving sends one by one: 5,000 of 16 KiB in 0.91 s (84.8).
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M5 of design 011. At first a link spent eight times quinn's CPU on a small
record: scans of the backlog, a system call and allocations a record, 19
bytes of framing. After the seven changes before this one, the transport
alone (transport.c; a backlog drained, every record checked) spends per
record 0.30 us for 61 bytes (quinn 0.27: 1.06 to 1.12 times over three
campaigns, at the design's 10 % line), 2.91 us for 1,013 bytes (quinn
3.88) and 45.2 us for 16,013 bytes (quinn 60.9): 25 % less for the larger
ones, and 30 % more records a second. What is left for small records is
per packet: the stream's names and the RECORDS head. quinn's numbers carry
no confirmation of storing and no exactly once.
Between two pure-serve nodes the links spend more per record, woken at
the receiving app's pace. Filling the sender showed the outbox is written
whole at every save, as the numbers heard were (094): the next thing to
change.
run.py gains --transport and --drain; the quinn service reads a drain a
chunk at a time and its client writes 64 KiB at a time.
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A record over a piece (1,000 bytes) went in pieces even when it fit the
packet whole: a record of 1,013 bytes went as two RECORD frames, and the
receiver gathered it the slow way (an allocation, pieces, then onto the
line). A record none of whose pieces went yet now goes whole in a RECORDS
frame whenever it fits what is left of the packet; its pieces are marked
sent together. A record too large for a packet, or one resent after
some of its pieces were lost, still goes in pieces, and a receiver takes
a record whole or in pieces alike.
The transport alone takes 2.85 us a record of 1,013 bytes, not 3.18
(quinn: 3.90). transport.c now checks every record delivered: in order,
once each, its bytes as sent. None was wrong in a network namespace with
1 ms of delay, 3 % loss and 10 % reordering, with records of 61, 1,013
and 16,013 bytes.
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Every queued record wrote the link's eventfd, a system call each, and woke
the thread to send a packet of a few records. A record queued now wakes
the thread only when it sleeps and nobody woke it yet; one queued while it
sends marks the link, and the thread looks again before it sleeps. With
records queued one at a time as fast as a thread can, 200,000 small ones
went at 400k a second, and now at 730k; queuing one costs 0.43 us, not
1.0.
research/experiments/019-idle-links/transport.c measures the transport
alone: a link and a listener in one process, no app, no store. A backlog
of 200,000 records of 61 bytes drains at 3 to 4 million a second, 0.24 us
a record on each side.
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M2 and M4 of design 011. Ten thousand devices send an order every five
seconds (2,000 a second); the receiver is killed (-9) at about 21 s and
started again at once. With its secrets remembered the node shows no
100 ms step without an order stored, catches up in 0.2 s, spends no more
CPU than before and makes no X25519; 34 orders were sent again, and
every order made was applied once (three rounds; on the SD card the
same, with 0.2 s silent). Without the memo it makes 10,000 X25519, 1.6 s
of CPU. quinn under the same load stops for 1.0 s and catches up after
10.9 s: 10,115 new connections, about 7 s more of the service's CPU and
8 s of the clients'. A first contact takes Pure one round trip and QUIC
two, at 10, 50 and 100 ms of RTT.
run.py --restart and --first-contact make them; the quinn harness gains
a fixed port with a reset key from its key, clients that connect again,
and a drain for M5.
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M1 of design 011. A Pure node allows 1,000 to 1,000,000 senders; each
sends one order and, once told it is stored, rests. At rest a link costs
the node 132 bytes (the sender allowed, 73; its number heard, about 60)
and no transport state; with a million the node runs in 139 MB. A quinn
0.11 service holding the same exchange's clients connected at rest costs
38,106 bytes a connection: 289 times as much, past the design's 1/100.
A link at rest takes its next record in 0.56 ms to stored, one X25519 on
the node included; a new QUIC connection takes 1.06 ms and 2.8 times the
receiver's CPU, without storing.
research/experiments/019-idle-links: links.c, many senders written from
serve/link.h's packet format alone (a second implementation), and the
quinn service and clients (quic/, built offline); run.py makes both
measurements.
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