4.7.5Interrupt Coalescing

The LSI Logic host adapters can complete multiple I/O requests per host interrupt. Interrupt coalescing is used to reduce CPU interrupts by pooling multiple disk command completions (I/O) into one interrupt. This feature may be enabled or disabled.

LSI Logic has performed significant testing under multiple I/O conditions and has determined that interrupt coalescing can be very valuable for small transfer lengths or random, transaction-oriented I/O workloads. For this type of workload, LSI Logic recommends that the Interrupt Coalescing values be set to a queue depth of 9, with a timeout of 1280 (0x500) ∝ s. This means that the host is interrupted only once for 9 I/Os processed by the chip, unless 1280 ∝ s have passed since the host was last interrupted. If the workload is of a large transfer length and sequential, LSI Logic recommends that interrupt coalescing be disabled to prevent performance degradation.

Although LSI Logic has determined that these settings are optimal for a wide variety of situations, your own I/O load may benefit from a deeper queue or a longer timeout. LSI Logic provides a mechanism to modify these values and write them to the nonvolatile EEPROM on the adapter.

Select the port or adapter shown (use the port name your system assigns):

ok select /pci@8,700000/IntraServer,fc@1

Then enter commands as shown in the following example:

ok show-interrupt-coalescing

Interrupt coalescing timeout is 500 (1280 decimal) microseconds

Interrupt coalescing depth is 9 (9 decimal)

ok set-interrupt-coalescing

Note: The OpenBoot BIOS provides help when you enter a command that does contain the proper arguments. In this case, OpenBoot responds with:

usage is <timeout><depth> set-interrupt-coalescing

ok 100 8 set-interrupt-coalescing

OpenBoot BIOS

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