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 From : Sergey Lentsov                       2:4615/71.10   19 Jan 2001  05:51:00
 To : All
 Subject : URL: http://lwn.net/2001/0118/kernel.php3
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    See also: [13]last week's Kernel page.
    
 Kernel development
 
    The current kernel release remains 2.4.0. Linus continues to put out
    2.4.1 prepatches; the 2.4.1 prepatch is in its eighth revision as of
    this writing. It contains a number of small fixes, Jens Axboe's block
    I/O scheduling improvements, and, as of pre4, the ReiserFS filesystem
    (see below). See Linus's [14]"half-assed changelog" for a quick list
    of the contents of this patch.
    
    Alan Cox continues to maintain his "ac" series, with the latest
    release being [15]2.4.0-ac9. This patch is rather more extensive than
    Linus's prepatch (7MB, as opposed to just over 1MB for 2.4.1-pre8).
    Much of what is there is the result of a late kernel code auditing
    frenzy by a number of people; many questionable things have been
    cleaned up.
    
    Linus's conservative approach to 2.4 patches is creating a large
    backlog of stuff waiting to go in. There will be quite a job of
    merging to do once Linus opens things up again.
    
    No 2.2 kernel prepatches have come out over the last week.
    
    Disk corruption with 2.4.0 and VIA IDE chipsets has been reported by
    some users. Evidently some VIA chips don't do DMA all that well,
    leading to [16]unhappy users who, hopefully, have good backups. The
    maintainer of the driver for VIA IDE is Vojtech Pavlik; his is
    currently [17]looking for trouble reports in order to be able to pin
    down just what the problem is. If you have VIA IDE and (1) have seen
    problems, or (2) are willing to do some testing, consider helping so
    that this problem can be eliminated.
    
    2.4.1-pre6 also had disk corruption problems due to a mistake in the
    ReiserFS merge. It was fixed quickly, but it's always good to have an
    occasional reminder that development kernels can be risky. Those who
    are interested can read [18]Linus's description of the problem and why
    he didn't notice it right away:
    
      With a gig of RAM, inodes tend to cache really well.
      
      Now, I'm not saying your filesystem is toast. I'm just saying that
      if you booted up in pre6, I'd suggest a quick reboot into a better
      kernel might be a good idea (be a jock, and do a sync and just push
      the reset button to force a proper fsck when it comes up - just in
      case).
      
    This problem was discussed as part of a thread on the virtual memory
    performance of the 2.4.1 prepatch series, which is generally
    considered to be inferior to 2.4.0.
    
    ReiserFS is in. Last week, remember, Linus [19]announced that he was
    going to be extremely conservative in accepting patches for 2.4:
    
      In order for a patch to be accepted, it needs to be accompanied by
      some pretty strong arguments for the fact that not only is it
      really fixing bugs, but that those bugs are _serious_ and can cause
      real problems.
      
    Some people were thus rather surprised to see a whole new filesystem
    show up in 2.4.1-pre4. It's hard to make the claim, after all, that
    the addition of ReiserFS is fixing a serious bug.
    
    [20]Linus's answer to this surprise is essentially (1) putting
    ReiserFS into 2.4.1 has been expected for some time; (2) people have
    been pounding on ReiserFS for quite some time - SuSE, for example, has
    included it for a while; (3) ReiserFS does not affect anything outside
    of the filesystem, and (4) no showstopper bugs have shown up, so
    there's no need for a pure bugfix release.
    
    So what is ReiserFS, anyway? This filesystem, created by Hans Reiser,
    has attracted interest in recent times due to its journaling
    capability - it can recover from a crash without the need for a
    lengthy filesystem checking pass. But journaling was not the original
    purpose behind ReiserFS - Mr. Reiser has much more ambitious plans
    than that. For details, have a look at [21]the ReiserFS writeup from
    the November 11, 1999 LWN Kernel Page. For many, many more details,
    set aside a block of time and visit the [22]Namesys home page.
    
    For those wanting to experiment with ReiserFS, bear in mind that NFS
    still can not serve files from a ReiserFS partition. There are patches
    in circulation to remove that limitation, but they have not yet made
    it into the kernel tree. (Yes, SuSE's 2.2 distribution features a
    working ReiserFS NFS, but those patches are not currently in the 2.4.1
    prepatch).
    
    Who's the fastest web server of all? One of the more controversial
    features of the 2.4 kernel is khttpd - the kernel HTTP (web) server.
    Not everybody believes that this sort of service belongs in the
    kernel. If it is there, however, it should produce good results.
    Christoph Lameter [23]decided to run some tests, using the Zeus
    benchmark, to compare khttpd's performance with boa, a user-space web
    server. His results:
    
                            Server Requests/second
                            khttpd             197
                             boa               591
                                       
    Thus, at a first glance, it would seem there's little reason to keep
    khttpd in the kernel. Of course, the version of khttpd that is in the
    2.4.0 kernel does not support persistent connections, which puts it at
    a disadvantage. But even when persistent connections were disabled for
    the test, boa came in with 227 requests per second - still more than
    khttpd.
    
    The story does not end there, however. The author of khttpd - Arjan
    van de Ven - has a patch which enables support of persistent
    connections; it just has been kept out of the kernel by the persistent
    feature freeze. Mr. Lameter [24]reran the tests with the patch applied
    and got a rather different set of results:
    
                            Server Requests/second
                            khttpd            1144
                             boa               591
                                       
    With persistent connections enabled, khttpd handles almost twice as
    many requests as boa; this would, one might think, end the discussion.
    
    Except, of course, that there is another kernel web server out there.
    Ingo Molnar decided it would be fun to run the same benchmark with the
    (upcoming) TUX 2.0 patch, along with the zero-copy networking patch
    (discussed [25]last week). [26]His results: 12,658 requests per
    second. It's worth noting that Ingo's test ran on different hardware.
    Nonetheless, TUX is looking pretty good...
    
    The quotes of Chairman Linux. Reading linux-kernel can be fun at
    times...
    
    [27]On device documentation:
    
      Once you realize that documentation should be laughed at, peed
      upon, put on fire, and just ridiculed in general, THEN, and only
      then, have you reached the level where you can safely read it and
      try to use it to actually implement a driver.
      
    and [28]his poor fortune:
    
      Oh, well. Not everybody can be as goodlooking as me. It's a curse.
      
    Other patches and updates released this week include:
    
      * A [29]logical volume manager (LVM) patch which fixes a number of
        bugs has been posted by Heinz J. Mauelshagen.
      * Christoph Lameter has released [30]a patch to khttpd which adds
        persistent connections and a number of other useful features.
      * Andreas Bombe has posted [31]an IEEE1394 ('firewire') patch which
        fixes a number of problems with the 2.4.0 implementation.
      * Daniel Quinlan has released [32]a cramfs patch which adds a number
        of new features to the compressed filesystem code.
      * For those interested in the various "hot-pluggable" peripherals
        under Linux, a new [33]Linux Hotplugging web site has just been
        set up.
        
    Section Editor: [34]Jonathan Corbet
    January 18, 2001
    
    For other kernel news, see:
      * [35]Kernelnotes
      * [36]Kernel traffic
      * [37]Kernel Newsflash
      * [38]Kernel Trap
    
    Other resources:
      * [39]Kernel Source Reference
      * [40]L-K mailing list FAQ
      * [41]Linux-MM
      * [42]Linux Scalability Project
    
    
    
                                                   [43]Next: Distributions
    
    [44]Eklektix, Inc. Linux powered! Copyright Щ 2001 [45]Eklektix, Inc.,
    all rights reserved
    Linux Ю is a registered trademark of Linus Torvalds
 
 References
 
    1. http://lwn.net/
    2. http://ads.tucows.com/click.ng/pageid=001-012-132-000-000-003-000-000-012
    3. http://lwn.net/2001/0118/
    4. http://lwn.net/2001/0118/security.php3
    5. http://lwn.net/2001/0118/dists.php3
    6. http://lwn.net/2001/0118/devel.php3
    7. http://lwn.net/2001/0118/commerce.php3
    8. http://lwn.net/2001/0118/press.php3
    9. http://lwn.net/2001/0118/announce.php3
   10. http://lwn.net/2001/0118/history.php3
   11. http://lwn.net/2001/0118/letters.php3
   12. http://lwn.net/2001/0118/bigpage.php3
   13. http://lwn.net/2001/0111/kernel.php3
   14. http://lwn.net/2001/0118/a/half-assed-changelog.php3
   15. http://lwn.net/2001/0118/a/2.4.0-ac9.php3
   16. http://lwn.net/2001/0118/a/via-example.php3
   17. http://lwn.net/2001/0118/a/via-ide.php3
   18. http://lwn.net/2001/0118/a/lt-toast.php3
   19. http://lwn.net/2001/0111/a/lt-2.4-policy.php3
   20. http://lwn.net/2001/0118/a/lt-reiserfs.php3
   21. http://lwn.net/1999/1111/kernel.php3
   22. http://www.namesys.com/
   23. http://lwn.net/2001/0118/a/cl-khttpd.php3
   24. http://lwn.net/2001/0118/a/cl-khttpd-persistent.php3
   25. http://lwn.net/2001/0111/kernel.php3
   26. http://lwn.net/2001/0118/a/im-tux.php3
   27. http://lwn.net/2001/0118/a/lt-documentation.php3
   28. http://lwn.net/2001/0118/a/lt-goodlooking.php3
   29. http://lwn.net/2001/0118/a/lvm.php3
   30. http://lwn.net/2001/0118/a/cl-khttpd-patch.php3
   31. http://lwn.net/2001/0118/a/firewire-patch.php3
   32. http://lwn.net/2001/0118/a/cramfs.php3
   33. http://linux-hotplug.sourceforge.net/
   34. mailto:lwn@lwn.net
   35. http://www.kernelnotes.org/
   36. http://kt.linuxcare.com/
   37. http://www.atnf.csiro.au/~rgooch/linux/docs/kernel-newsflash.html
   38. http://www.kerneltrap.com/
   39. http://lksr.org/
   40. http://www.tux.org/lkml/
   41. http://www.linux.eu.org/Linux-MM/
   42. http://www.citi.umich.edu/projects/linux-scalability/
   43. http://lwn.net/2001/0118/dists.php3
   44. http://www.eklektix.com/
   45. http://www.eklektix.com/
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  * Origin: Unknown (2:4615/71.10@fidonet)
 
 

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