On Tue, Jun 12 2007, Tejun Heo wrote: > Arjan van de Ven wrote: > >> I'm not sure about this. We need better PM framework to support > >> powersaving in other controllers and some ahcis don't save much > >> when only link power management is used, > > > > do you have data to support this? > > Yeah, it was some Lenovo notebook. Pavel is more familiar with the > hardware. Pavel, what was the notebook which didn't save much power > with standard SATA power save but needed port to be completely turned off? > > > The data we have from this patch is that it saves typically a Watt of > > power (depends on the machine of course, but the range is 0.5W to > > 1.5W). If you want to also have an even more agressive thing where > > you want to start disabling the entire controller... I don't see how > > this is in conflict with saving power on the link level by "just" > > enabling a hardware feature .... > > Well, both implement about the same thing. I prefer software > implementation because it's more generic and ALPE/ASP seems too > aggressive to me. Here are reasons why sw implementation wasn't merged. > > 1. It didn't have proper interface with userland. This was mainly > because of missing ATA sysfs nodes. I'm not sure whether adding this to > scsi node is a good idea. > > 2. It was focused on SATA link PS and couldn't cover the Lenovo case. > > I think we need something at the block layer. I think the hardware method is preferable, actually. Doing this in the block layer would mean keeping track of idle time, and that quickly turns into a lot of timer management. Not exactly free, in terms of CPU usage. I've yet to do some power measurements with this ahci patch, I just noticed that with min_power performance drops from ~55mb/sec to ~15mb/sec sequential on my drive. That's pretty drastic :-) -- Jens Axboe - To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
