Contents Telektronikk - Telenor

Time [ms]
Time [ms]
3.6
3.2
2.8
2.4
2.0
1.6
1.2
.8
.4
0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
.8
.4
0
0
0
SBA-200/2.2.6 - driver
SBA-200/2.2.6 - total
SBA-100/2.2.6 - driver
SBA-100/2.2.6 - total
SBA-100/2.0 - driver
SBA-100/2.0 - total
SBA-200/2.2.6 - driver
SBA-200/2.2.6 - total
SBA-100/2.2.6 - driver
SBA-100/2.2.6 - total
not fully representative for performance
when the protocol operates like stop-andgo.
In order to explain the Sparc2 and
Sparc10 relative performance for smaller
window sizes when using SBA-100
adapters, we measured the throughput
with TCP operating as a stop-and-go protocol
for these configurations. This was
achieved by setting the window size
equal to the user data size. The throughput
under such a behavior is shown in
Figure 5 for both host architectures. Up
to a user data size between 2048 and
2560 bytes the slower Sparc2 has a higher
throughput. This is most likely due to
the longer Sbus access time combined
with the relatively longer interrupt time.
4 Initial throughput
measurements
2048 4096 6144 8192
Segment size [byte]
(a) Sparc2 send times
2048 4096 6144 8192
Segment size [byte]
(c) Sparc10 send times
This section presents the initial throughput
measurements for the reference architecture,
the Sparc2 with the SBA-100
network adapter with the first network
driver version, i.e. version 2.0. Figure 6
(a) presents the measured TCP end-toend
memory-to-memory throughput for
Time [ms]
Time [ms]
3.6
3.2
2.8
2.4
2.0
1.6
1.2
.8
.4
0
3.6
3.2
2.8
2.4
2.0
1.6
1.2
.8
.4
0
0
0
SBA-200/2.2.6 - driver
SBA-200/2.2.6 - total
SBA-100/2.2.6 - driver
SBA-100/2.2.6 - total
SBA-100/2.0 - driver
SBA-100/2.0 - total
SBA-200/2.2.6 - driver
SBA-200/2.2.6 - total
SBA-100/2.2.6 - driver
SBA-100/2.2.6 - total
Figure 4 Segment send and receive processing times
different user data sizes and different
window sizes. The throughput dependent
on window size for a fixed user data size
of 8192 bytes is presented in Figure 6
(b), and the corresponding CPU utilization
in Figure 6 (c). Both the user data
size and the window size affect measured
throughput. From the graphs it is clear
that increasing the TCP window size
above 32 kbytes has no increasing effect
on the throughput. On the contrary, such
an increase in window size results in a
significantly varying throughput dependent
on user data size. The reason is cell
loss at the receiving host which causes
TCP packet loss and retransmissions of
lost packets.
In general, the receive operation is
known to be more time consuming than
the transmit operation. At the receive
side, there are among other things
demultiplexing and scheduling points
and interrupts which do not occur at the
send side. In addition, reading from
memory is more time consuming than
writing to memory. Clearly, this is evident
from the driver processing times
presented in Figure 4. Furthermore, the
processor (CPU) utilization histograms in
2048 4096 6144 8192
Segment size [byte]
(b) Sparc2 receive times
2048 4096 6144 8192
Segment size [byte]
(d) Sparc10 receive times
Figure 6 (c) show the receiver to be
heavier loaded than the sender. When the
TCP connection starts losing packets due
to cell loss at the receiver, both the
throughput and CPU utilization are
degraded. TCP employs positive
acknowledgment with go-back-n retransmission.
The sender fills the window,
and if every byte is not acknowledged, it
relies on retransmission timers to go off
before it starts sending at the point of the
Throughput |Mbit/s]
30
20
10
Sparc2
Sparc10
0
0 1024 2048 3072 4096
user data = window = segment size [byte]
Figure 5 Sparc2 versus Sparc10 segment
processing, SBA-100/2.2.6
159