Hi Tejun, On Thu, Sep 11, 2008 at 12:34 PM, Tejun Heo <tj@xxxxxxxxxx> wrote: > Hello, Shem Multinymous. >> Using the input device interface for the accelerometer (as done by >> tp_smapi's hdaps + latest hdapsd) greatly reduces the number of >> accelerometer-related timer interrupts on tickless kernels, as >> measured by powertop. With syscall polling you have the kernal polling >> the hardware at ~50Hz and then the userspace hdapsd polling the kernel >> at ~50Hz. When they're out of phase so you can get up to 100 >> interrupts/sec. With an input device you're always at 50Hz. The phase >> difference also induces a small extra delay in the shock handling >> response. > > That reduction comes because input device supports poll and > sysfs_notify_event() does about the same thing. The uesrland daemon > can just poll on a node and read data nodes when poll event on the > node triggeres. Agreed. There's another issue with the current sysfs interface, though: hdapsd needs to read (x,y,timestamp) tuples, whereas sysfs provides just x and y in separate attributes which cannot be read atomically together. We can add a sysfs file with "x y timestamp" readouts, though this is unusual for sysfs (and certainly incompatible with hwmon). > Unloading heads will be simple. Just echoing timeout in ms to sysfs > nodes, so I don't think it's a good idea to push out actual unloading > to another process especially as fork doesn't inherit mlockall. I had in mind another daemon listening for "unload now" events, so no forking needed. This second daemon might make sense if we push the logic of deciding *which* disks to unload into userspace, since this logic is the same for the ThinkPad style and the HP style. > On a related note, is there any plan to merge tp_smapi to mainline? > It seems you put a lot of work into it and I don't really see why it > should stay out of tree. The only issue I'm aware of is finding a reasonably-named maintainer. On the technical side, the reviews on my lkml submission of thinkpad_ec+hdaps seemed good and all technical comments are since addressed. The code has been stable, well-tested and packaged by major distros for years. Shem -- 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
