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Jens Axboe On Kernel Development

Posted by ScuttleMonkey on from the nuts-and-bolts dept.

BlockHead writes "Kerneltrap.org is running an interview with Jens Axboe, 15 year Linux veteran and the maintainer of the linux kernel block layer, 'the piece of software that sits between the block device drivers (managing your hard drives, cdroms, etc) and the file systems.' The interview examines what's involved in maintaining this complex portion of the Linux kernel, and offers an accessible explanation of how IO schedulers work. Jens details his own CFQ, or Complete Fair Queue scheduler which is the default Linux IO scheduler. Finally, the article examines the current state of Linux kernel development, how it's changed over the years, and what's in store for the future."

9 of 68 comments (clear)

  1. Khmm... Block devices? How quaint! by mi · · Score: 2, Informative

    FreeBSD dispensed with them altogether years ago...

    Character devices only, thank you very much.

    *Duck*

    --
    In Soviet Washington the swamp drains you.
  2. CFQ not the default scheduler? by rehabdoll · · Score: 4, Informative

    Anticipatory is, according to my menuconfig:

    The anticipatory I/O scheduler is the default disk scheduler. It is
    generally a good choice for most environments, but is quite large and
    complex when compared to the deadline I/O scheduler, it can also be
    slower in some cases especially some database loads.    *

    Anticipatory is also preselected with a fresh .config

    1. Re:CFQ not the default scheduler? by darkwhite · · Score: 2, Informative

      CFQ was committed relatively recently and there was discussion for a while as to whether and when to make it default. I think 2.6.19 uses Anticipatory by default, but 2.6.20 will use CFQ by default (not 100% sure though).

      --

      [an error occurred while processing this directive]
    2. Re:CFQ not the default scheduler? by zdzichu · · Score: 4, Informative

      CFQ is default since 2.6.18, released back in September 2006.

      --
      :wq
  3. Re:Missing Question: How do you pronounce your nam by Ysangkok · · Score: 2, Informative
    Well, he's a Dane. I'm a Dane too so I'll tell you how I would pronounce it:

    Jens is NOT pronounced "Djens". "J" is pronounced as a Palatal approximant in Danish - just like "y" in English. Yens is somewhat more correct, but the "e" has to be pronounced like the IPA [æ]. Danish is not logic at all. If it was, "Jens" would be spelled with a "æ". Take a look at Jens.

    IPA: [jæns]

    Axboe is more complicated:

    • A is pronounced flat. (like when you say "aah" at the dentist. Just like "spa". Take a look at Open back unrounded vowel)
    • X is pronounced "ks". When the word is pronounced quickly it may sound like "gs".
    • B is b.
    • "Oe" is usually pronounced like the Danish "ø". See Close-mid front rounded vowel

    IPA transcription of Axboe would be something like: Open back unrounded vowel + [ksbø]

    (I can't get the IPA sign for "Open back unrounded vowel" to display in Slash)

  4. Err, no by Fweeky · · Score: 2, Informative

    "It sounds like, by eliminating block devices, that they basically remove the kernel from doing any re-ordering or caching of data, which makes things "safer""

    No; FreeBSD's shifted the buffer cache away from individual devices and into the filesystem/VM, where it caches vnodes rather than raw data blocks. The IO queue (below all this block/character/GEOM stuff) is scheduled using a standard elevator algorithm called C-LOOK. It's showing it's age in places, and there's been some effort towards replacing/improving it, making it pluggable etc (e.g. Hybrid); sadly it's a tricky problem to solve properly. See this recent thread.

  5. Re:Wow ... by Error27 · · Score: 3, Informative

    Marcello was only 18 when he took over the 2.4 branch. He was working for Conectiva at age 13 or 14... Debian has had a bunch of really young package maintainers for critical packages.

  6. Re:Missing Question: How do you pronounce your nam by axboe · · Score: 3, Informative

    Hi John!

    That is correct, like a "y", rhymes with "mens". I saw another question on the lastname, I typically tell foreigners that it is pronounced ax-bow. Europeans often think the 'oe' is like the Danish "ø", however that is not the case.

  7. Re:Scheduling better than no scheduling? by axboe · · Score: 3, Informative

    It depends on what you need to schedule. If your drive does queuing and only one process IO is active, then the OS can do very little to help. The OS usually has a larger depth of ios to work with, so it's still often beneficial to do some sorting at that level as well.

    IO scheduling is a lot more than that, however. If you have several active processes issuing IO, the IO scheduler can make a large difference to throughput. I actually just did a talk at LCA 2007 with some results on this, you can download the slides here:

    LCA2007 CFQ talk