IBM PowerLinux information

Multiple Message Signaled Interrupts support

The PCI Express 3.0 (PCIe3) SAS adapter family supports multiple Message Signaled Interrupts Extension (MSI-X). This support allows the adapter device driver to process multiple interrupts in different processors in parallel, thus potentially improving the system performance. Increasing the number of interrupts that are used by an adapter might improve disk performance by increasing the disk throughput (or I/O), but it might also increase the usage of kernel resource. The ideal number of MSI-X interrupts must not be more than the number of RAID arrays optimized on a single adapter or the number of physical processors that are assigned to the system partition. The default value for the number of MSI-X interrupts is 2 and the maximum value is 15.

Changing the number of MSI-X interrupts

The number of MSI-X interrupts can be changed by changing the number_of_msix ipr module parameter, by using one of the following methods:

Add the ipr.number_of_msix=N argument to the kernel command line.
Create a file in the /etc/modprobe.d/ directory with the options ipr number_of_msix=N argument and then use mkinitrd to rebuild the initial ram disk image.

In both these options, the value of N is in the range 2 - 15.

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Last updated: Mon, August 12, 2013