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28 CR12/CT12, VR12/VP12 UEFI Firmware User's Guide
Publication No. UGCR12V051E Rev. A.0
4.4.10
No Snoop
The optimal default is
Enabled
.
If the area of memory a PCI‐E device accesses is not cached by the processor,
enabling this option might result in improved latency by eliminating unnecessary
snoop actions. An example of that might be large data structures (texture maps,
Vertex arrays) written by CPU and read by GPU. However, in certain cases data may
still be snooped.
NOTE
If user recognizes data coherence issues disabling this feature might help.
4.4.11
Maximum Payload
The optimal default is
Auto
.
This feature defines the size of actual data that can be transferred within a single
transaction layer packet (TLP) along the PCI‐Express bus.
During SBC initialization phase (power on, reset) the devices capabilities structure is
queried and the highest supported Maximum Payload size for all devices is
determined. However, this is subject to all PCI‐Express devices connected support at
minimum the selected Maximum Payload size.
If user set this feature to a lower value, all connected PCI‐Express devices will be
forced to use the selected Maximum Payload size, even if all devices would support
a much larger payload size.
A larger size would increase the theoretical throughput as more data would be
payload rather than protocol overhead. Adjusting this feature to lower size may
improve latency especially for lower bandwidth devices e.g. (VME controller).
Customer should benchmark his system performance to determine the optimal
Maximum Payload.
When set to Auto, a default value with maximum fairness and optimal performance
is used.
NOTE
Customer should benchmark his system performance to determine the optimal Maximum Payload size.
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