[lkml]   [2007]   [Jun]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: [patch 0/3] AHCI Link Power Management
    Tejun Heo wrote:
    >> 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?

    Pavel, if you have time, could you measure this with Kristen's patch?

    >> 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.

    Too aggressive in what way?

    There are tradeoffs on either side. Doing things in software is more
    work for the cpu, and depending on the implementation, will consume
    more power on the CPU side. (for example if you need regular timers
    that just consumes the power you are saving back up). The hardware can
    obviously switch very fast (because it's independent of any software),
    yet of course the software has higher level knowledge about how idle
    the link really is (like it knows if any files are open etc etc).

    To be honest, I would be surprised if software could do significantly
    better than hardware though; it seems a simple problem: Idle -> go to
    low power, and estimating idle isn't all that hard on a link level...
    there's not all THAT much the kernel can estimate better I suspect.

    This debate is very similar to the cpufreq debate from 4 years ago,
    where there were 3 levels: do it in the CPU, do it in the kernel or do
    it in userspace. All three are valid; whichever is best depends on the
    exact hardware that you have...
    (and you can argue that first everyone started in userspace, then the
    hardware improved that made a kernelspace implementation better
    (ondemand) and now Turbo Mode is more or less moving this to the
    hardware... I wouldn't be surprised if the sata side will show a
    similar trend)
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to
    More majordomo info at
    Please read the FAQ at

     \ /
      Last update: 2007-06-12 06:23    [W:0.022 / U:44.264 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site