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Solarflare Server Adapter User Guide
Solarflare Adapters on Windows
Issue 20 © Solarflare Communications 2017 230
Port mode
The selected port mode for SFN7000 and SFN8000 series adapters should
correspond to the speed and number of connectors in use, after using any splitter
cables. If a restricted set of connectors is configured, the driver can then transfer
resources from the unused connectors to those configured, potentially improving
performance.
Max Frame Size
The default maximum frame size ensures that the adapter is compatible with legacy
10/100Mbps Ethernet endpoints. However if a larger maximum frame size is used,
adapter throughput and CPU utilization can be improved. CPU utilization is
improved, because it takes fewer packets to send and receive the same amount of
data. Solarflare adapters support maximum frame sizes up to 9216 bytes (this does
not include the Ethernet preamble or frame check sequence).
NOTE: The maximum frame size setting should include the Ethernet frame header.
The Solarflare drivers support 802.1p. This allows Solarflare adapters on Windows
to optionally transmit packets with 802.1Q tags for QoS applications. It requires an
Ethernet frame header size of 18 bytes (6 bytes source MAC address, 6 bytes
destination MAC address, 2 bytes 802.1Q tag protocol identifier, 2 bytes 802.1Q
tag control information, and 2 bytes EtherType). The default maximum frame size
is therefore 1518 bytes.
Since the maximum frame size should ideally be matched across all endpoints in the
same LAN (VLAN), and since the LAN switch infrastructure must be able to forward
such packets, the decision to deploy a larger than default maximum frame size
requires careful consideration. It is recommended that experimentation with
maximum frame size be done in a controlled test environment.
The maximum frame size is changed by changing the Max Frame Size setting in the
Network Adapter’s Advanced Properties Page.
Interrupt Moderation (Interrupt Coalescing)
Interrupt moderation reduces the number of interrupts generated by the adapter by
coalescing multiple received packet events and/or transmit completion events
together into a single interrupt.
The interrupt moderation interval sets the minimum time (in microseconds)
between two consecutive interrupts. Coalescing occurs only during this interval:
• When the driver generates an interrupt, it starts timing the moderation
interval.
• Any events that occur before the moderation interval expires are coalesced
together into a single interrupt, that is raised only when the interval expires.
A new moderation interval then starts, during which no interrupt is raised.
• An event that occurs after the moderation interval has expired gets its own
dedicated interrupt, that is raised immediately.
A new moderation interval then starts, during which no interrupt is raised.