HP IO Accelerator for BladeSystem c-Class - Manual (Page 21)

Performance and tuning 21
Performance and tuning
Introduction to performance and tuning
HP IO Accelerator devices provide high bandwidth and high IOPS and are specifically designed to achieve
low latency.
As IO Accelerator devices improve in IOPS and low latency, the device performance may be limited by
operating system settings and BIOS configuration. To take advantage of the revolutionary performance of IO
Accelerator devices, you might have to tune these settings.
While IO Accelerator devices generally perform well out of the box, this section describes some of the
common areas where tuning may help achieve optimal performance.
Disabling DVFS
DVFS is a power management technique that adjusts the CPU voltage and frequency to reduce power
consumption by the CPU. These techniques help conserve power and reduce the heat generated by the CPU,
but they adversely affect performance while the CPU transitions between low-power and high-performance
states.
These power-savings techniques are known to have a negative impact on I/O latency and maximum IOPS.
When tuning for maximum performance, you might benefit from reducing or disabling DVSF completely,
even though this might increase power consumption.
DVFS, if available, should be configurable as part of your operating systems power management features as
well as within your system BIOS interface. Within the operating system and BIOS, DVFS features are often
found under the ACPI sections. Consult your computer documentation for details.
Limiting APCI C-states
Newer processors have the ability to go into lower power modes when they are not fully utilized. These idle
states are known as ACPI C-states. The C0 state is the normal, full power, operating state. Higher C-states
(C1, C2, C3, and so on) are lower power states.
While ACPI C-states save on power, they are known to have a negative impact on I/O latency and maximum
IOPS. With each higher C-state, typically more processor functions are limited to save power, and it takes
time to restore the processor to the C0 state.
These power savings techniques are known to have a negative impact on I/O latency and maximum IOPS.
When tuning for maximum performance you might benefit from limiting the C-states or turning them off
completely, even though this might increase power consumption.
If your processor has ACPI C-states available, you can typically limit or disable them in the BIOS interface
(sometimes referred to as a Setup Utility). APCI C-states might be part of the ACPI menu. For details, see your
computer documentation.