Here's a set of patches which implement link power management for SATA. We had talked at kernel summit of moving sysfs interface for setting the link power management policy to the block layer, but after a lot of consideration, I think this doesn't make sense. Mainly because I feel for SATA the link power management policy should be associated with the controller, not with the device. So, we continue to use the shost_attrs array in the scsi host template to create a sysfs interface that is associated with the scsi_host class. These patches have changed since the last version. The patches have been refreshed to use the new ata_link structures. Additionally, I've separated out DIPM enabling and put it into libata-core, because DIPM can be used by any SATA disk that is attached to a controller which allows DIPM, although in this implementation the driver will need to explicitly set a flag which would indicate to the core that it is OK to set DIPM. This is because all interface power state changes can cause Phy Ready interrupts, and the driver will need to know to ignore them. DIPM will only be enabled for the min_power link power management policy value. This is because many disks are not clever enough to know that if a controller naks their request for a SLUMBER transition, they should retry for PARTIAL - instead they will just give up all together. With these patches, measured on my X60 with a Watts Up Pro meter, in the base station after all powertop suggestions have been applied, I see a savings of approximately .7-.8 W in min_power mode, and .5 W in medium_power mode. For the best power/performance tradeoff, it's recommended that you use the "medium_power" setting, although min_power can be used of course when you absolutely need to save every 10th of a watt and don't care about the additional performance loss. Please give them a try. Thanks, Kristen - To unsubscribe from this list: send the line "unsubscribe linux-ide" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
