Dell Emulex Family of Adapters - Manual (Page 664)

Emulex Drivers for Windows User Manual P010077-01A Rev. A
3. Configuration
iSCSI Driver Configuration
664
Interrupt Moderation Policy Settings
The Interrupt Moderation policy settings control the rate of interrupts for UCNA
hardware. By default, the driver implements an interrupt moderation scheme that is
based on the I/O load and the interrupt rate. The default setting for im_policy tries to
vary the interrupt rate between 3500 to 10000 interrupts per second. In addition, the
iSCSI driver allows other configuration settings, as shown in Table 3-13.
While the default setting may work for most configurations, there are instances when
the setting may need to be altered. The im_policy parameter setting should be based on
the UCNA system configuration, the number of iSCSI targets to be connected, the I/O
load, and the throughput and latency offered by these iSCSI targets.
On systems that are capable of sustaining a higher interrupt rate and on which the
number of connected targets is low (eight or fewer), setting the im_policy to 1 results in
lower latency and higher values of I/O operations per second (IOPs). But this
aggressive interrupt rate can also result in system stalls and freezes, especially if queue
depth values are high and I/O requests are small.
In a configuration that involves a large number of iSCSI targets (more than 32 or 64)
and higher values of queue depth, the default setting may prove to be too aggressive. In
such a case, you may need to change the im_policy parameter setting to 3 or 4.
Although this increases latency of an I/O request, the lower interrupt rate may allow
the system to be functional under a high load.
Creating Non-Bootable Targets
To set up non-bootable targets, proceed with the driver and operating system
installation, then download and use the Microsoft iSCSI Initiator Service to configure
and manage the adapter.
Using the Microsoft iSCSI Initiator Service
You can use the Microsoft iSCSI Initiator Service to configure and manage the UCNA.
The Microsoft Initiator Service is available as a free download from
www.microsoft.com. See the documentation that accompanies it for detailed
information.
Note: When you install the Microsoft iSCSI Initiator Service, you need to select only
the Initiator Service check box and not the Software Initiator check box.
Table 3-13 im_policy Settings
Parameter Value Setting Description
im_policy=0 Disabled The Interrupt rate algorithm is turned off in the driver.
im_policy=1 Aggressive The highest interrupt rate.
im_policy=2 Moderate The default value.
im_policy=3 Conservative A lower interrupt rate than moderate.
im_policy=4 Very conservative The lowest interrupt rate.