Emulex 3.3 Server Performance (Windows)

The HBAnyware Utility User Manual Page 80

Server Performance (Windows)

I/O Coalescing is enabled and controlled by two driver parameters: CoalesceMsCnt and

CoalesceRspCnt. The effect of I/O Coalescing will depend on the CPU resources available on the

server. With I/O Coalescing turned on, interrupts are batched, reducing the number of interrupts and

maximizing the number of commands processed with each interrupt. For heavily loaded systems, this

will provide better throughput.

With I/O Coalescing turned off (the default), each I/O processes immediately, one CPU interrupt per I/O.

For systems not heavily loaded, the default will provide better throughput. The following table shows

recommendations based upon the number of I/Os per HBA.

CoalesceMsCnt

The CoalesceMsCnt parameter controls the maximum elapsed time in milliseconds that the HBA waits

before it generates a CPU interrupt. The value range is 0 - 63 (decimal) or 0x0 - 0x3F (hex). The default

is 0 and disables I/O Coalescing.

CoalesceRspCnt

The CoalesceRspCnt parameter controls the maximum number of responses to batch before an

interrupt generates. If CoalesceRspCnt expires, an interrupt generates for all responses collected up to

that point. With CoalesceRspCnt set to less than 2, response coalescing is disabled and an interrupt

triggers for each response. The value range for CoalesceRspCnt is 1 - 255 (decimal) or 0x1 - 0xFF

(hex). The default value is 8.

There are four driver parameters that must be considered (and perhaps changed from the default) for

better performance testing: QueueDepth, NumFcpContext, CoalesceMsCnt and CoalesceRspCnt.

QueueDepth

If the number of outstanding I/Os per device is expected to exceed 32, increase this parameter to a

value greater than the number of expected I/Os per device, up to a maximum of 254.The QueueDepth

parameter defaults to 32. If 32 is set and not a high enough value, performance degradation may occur

due to Storport throttling its device queue.

Table 9: Recommended Settings for I/O Coalescing

I/Os per Second Suggested

CoalesceMsCnt Suggested

CoalesceRspCnt

I/Os < 10000 0 8

10000 < I/Os < 18000 1 8

18000 < I/Os < 26000 1 16

!/Os > 26000 1 24

Note: A system restart is required to make changes to CoalesceMsCnt and/or CoalesceRspCnt.

Note: Parameter values recommended in this topic are for performance testing only and not

for general operation.