[SCSI] lpfc 8.1.1 : Add polled-mode support
- Add functionality to run in polled mode only. Includes run time attribute to enable mode. - Enable runtime writable hba settings for coallescing and delay parameters Customers have requested a mode in the driver to run strictly polled. This is generally to support an environment where the server is extremely loaded and is looking to reclaim some cpu cycles from adapter interrupt handling. This patch adds a new "poll" attribute, and the following behavior: if value is 0 (default): The driver uses the normal method for i/o completion. It uses the firmware feature of interrupt coalesing. The firmware allows a minimum number of i/o completions before an interrupt, or a maximum time delay between interrupts. By default, the driver sets these to no delay (disabled) or 1 i/o - meaning coalescing is disabled. Attributes were provided to change the coalescing values, but it was a module-load time only and global across all adapters. This patch allows them to be writable on a per-adapter basis. if value is 1 : Interrupts are left enabled, expecting that the user has tuned the interrupt coalescing values. When this setting is enabled, the driver will attempt to service completed i/o whenever new i/o is submitted to the adapter. If the coalescing values are large, and the i/o generation rate steady, an interrupt will be avoided by servicing completed i/o prior to the coalescing thresholds kicking in. However, if the i/o completion load is high enough or i/o generation slow, the coalescion values will ensure that completed i/o is serviced in a timely fashion. if value is 3 : Turns off FCP i/o interrupts altogether. The coalescing values now have no effect. A new attribute "poll_tmo" (default 10ms) exists to set the polling interval for i/o completion. When this setting is enabled, the driver will attempt to service completed i/o and restart the interval timer whenever new i/o is submitted. This behavior allows for servicing of completed i/o sooner than the interval timer, but ensures that if no i/o is being issued, then the interval timer will kick in to service the outstanding i/o. Signed-off-by: NJames Smart <James.Smart@emulex.com> Signed-off-by: NJames Bottomley <James.Bottomley@SteelEye.com>
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