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CONFIG_DEVTMPFS=y does not seem to be doing anything

Helmut Forren
Mastermind 6805 points


I'm experimenting with CONFIG_DEVTMPFS per the advice on page 36 of http://free-electrons.com/pub/conferences/2011/genivi/boot-time.pdf .  My additional research mentions CONFIG_DEVTMPFS_MOUNT and CONFIG_TMPFS.

My custom DM6467 was derived from the EVM, I'm using Linux kernel version 2.6.32 and dvsdk 3.10.00.11.  In the .config I find CONFIG_TMPFS=y already, and I changed a not set to CONFIG_DEVTMPFS=y.  I can't find a CONFIG_DEVTMPFS_MOUNT.

Now, when I boot, I can't find a difference in the console log from before and after this change, and the total boot is unchanged.  I also can't find notice of "ram" or "tmpfs" in the console log.

Did I do something wrong?  Through various methods, I've reduce my power-on-to-codec-running-video-out boot up time from 137sec to 52sec, but I need to go even shorter.

Note also that my reference above says "Remove udev..." at the same time as it says "Use devtmpfs...".  My intend in using CONFIG_DEVTMPFS=y was to effect this removal of udev.  Did I misunderstand?  Do I need to do something ELSE explicitly to remove udev?  I have gotten udev down from 25 seconds to 2.245 seconds, but want to reduce it further.  (Upon writing this, I realize it has gone from 25/137=18% of my boot time to 2.256/52=4.3% of my boot time, and that I should perhaps sleep on it and reanalyze my slow points again tomorrow.  Nevertheless, the question remains.  Perhaps devtmpfs will offer other speedups if I do it right.)

Thanks very much

P.S. I'm simultaneously trying out other speedup advice at http://e2e.ti.com/support/embedded/linux/f/354/t/177161.aspx#637937

  • 0
    Mastermind 6805 points

    Does anyone have any ideas on this?  Thanks.

  • 0
    Guru 26430 points

    I checked in the oldest TI kernel I have around, 3.20.00.14. The CONFIG_DEVTMPFS_MOUNT option is right after the CONFIG_DEVTMPFS option.

    Device Drivers
    ->Generic Driver Options
    --->Create a kernel maintained /dev tmpfs (EXPERIMENTAL)
    --->Automount devtmpfs at /dev

    The "Automount" option should appear when the "Create" option is selected. The options are in drivers/base/Kconfig.

    Never used DEVTMPFS. Getting the kernel to automatically create device files in a RAM paritition sounds promising. Not sure what happens with drivers loaded after boot though.