An Investigation into Transport Protocols and Data Transport ...

A.2. Network Interface Cards 286
CPU Kernel Utilisation (percent)
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1472 bytes
CPU Kernel Utilisation (percent)
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0
0 5 10 15 20 25 30 35 40
Interpacket Wait-Time (usec)
(a) Syskonnect
0
0 5 10 15 20 25 30 35 40
Interpacket Wait-Time (usec)
(b) Intel
Figure A.13: CPU Kernel utilisation of 1Gb/sec NIC cards (66Mhz in 64-bit PCI
buses).
Therefore, to achieve the same throughput with small packet size more
interrupts per unit time are required unless interrupts are generated as a
function of time. This would explain the decrease in throughput as a result
of using smaller packet sizes.
Figure A.13 shows the CPU utilisation of the kernel (networking) thread
for the 1Gb/sec Syskonnect and Intel cards as tested in Figure A.10. It shows
that the cleaner throughputs achieved by the Intel card also correlate to a
much lower CPU utilisation compared to that of the Syskonnect card. This,
combined with the high latencies experienced suggests that interrupt coalescing
is indeed being utilised by the Intel driver, whilst the high utilisation
of the Syskonnect driver affects stable high capacity throughput due to the
lack of CPU cycles to service the packets.
A.2.5
Summary
With suitable hardware, it was shown that Network Interface Cards are capable
of delivering close to the performance expected. Related work [GB02]
also demonstrates the capability of delivering Gigabit rates with suitable