Alex Hornung <ahorn...@gmail.com> wrote: > Hi, > > I've been playing around today to see the our power efficiency on my > ThinkPad. I have been using acpiconf -i 0 to see the discharge rate, and > it seems we can't get below 19W. On linux and Windows I can get as low > as 10-12W. > > I've set the brightness to the lowest level. I didn't enable any wifi > power management, but on linux I can't do that either since it has been > marked as broken for my card on linux (iwl3945). > > I've set the P-State to be fixed at 1GHz (the lowest), since powerd > doesn't seem to work correctly; it didn't seem to scale down from 2GHz > anymore after a while on an idle system. FWIW, estd seems to do a better > job, though. In any case discussing the sense or lack thereof behind > powerd is not the subject of this mail. > > I've also set the lowest C-state to C3 and according to > hw.acpi.cpu*.cx_usage, it is actually spending most of the idle time in > C3 (around 75%). > > Additionally I've set the ahci link power management to aggressive. This > is the biggest problem. While it seems to save another watt or so, it > also causes a long wait for even a simple ls if the stuff isn't cached. > dmesg shows timeouts: > ahci0.0: CMD TIMEOUT state=5 slot=22 > cmd-reg 0xc00d617<ASP,ALPE,CR,FR,FRE,POD,SUD,ST> > sactive=00400000 active=00000000 expired=00000000 > sact=00400000 ci=00000000 > STS=150 > ahci0.0: disk_rw: timeout > > This definitely doesn't occur on linux with ahci aggressive link power > management, and would seem like quite a big issue. Anyone knows why > these timeouts occur with aggressive link power management?
I didn't see those on my thinkpad when adding link power management. It looks like a bug. Are you getting those for each request, or just when activating it? What exact type of thinkpad and harddrive do you use? > > I'm also wondering what we need to do to increase our power efficiency > to a Linux-like level, or at least down to 15W on this ThinkPad. > > It would also be helpful if we could gather more information on why we > are so power inefficient. Can we see the number of wakeups per second > and what causes the wakeups, much like powertop on linux does? I played around with it a bit and to me it seemed that wakeups are not that much of a big deal. E.g. decreasing HZ (just for testing) didn't gain much. But I might be missing something as everyone in Linux-land talks about reducing the wakups and tickless kernels. Cheers, Johannes
