Re: Read Copy Update

From: Jeff Roberson (jroberson_at_mail.chesapeake.net)
Date: 02/19/04

  • Next message: Doug Rabson: "Re: Read Copy Update" 
    Date: Wed, 18 Feb 2004 18:26:05 -0500 (EST)
To: Doug Rabson <dfr@nlsystems.com>

    On Wed, 18 Feb 2004, Doug Rabson wrote:

    > So, I was reading the latest installment of the SCO soap on slashdot
    > today (bizarre - they seem to be claiming that they own all code that
    > was ever linked to a System V kernel) and I ended up trying to figure
    > out exactly what this RCU thing is that they claim is infringing their
    > right to obtain money with menaces.
    >
    > I read one of the original papers at
    > http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf and its a
    > surprisingly simple idea. Basically for certain data structures which
    > are read-mostly, you can make the entire read path lock-free at the
    > expense of making updates quite a bit more expensive. They claim that
    > its much faster than reader-writer locks both for light contention and
    > for heavy contention.
    >
    > I imagine that a FreeBSD implementation of RCU wouldn't actually be too
    > hard and it might be well worth it as an alternative way of managing
    > concurrency, e.g. for the routing cache and the name cache (and probably
    > lots of other things).
    >

    I've looked into this a bit myself. My general feeling is that it would
    not be terribly difficult to do, but I would prefer to start with stronger
    primitives and work our way into more efficient mechanisms. I say this
    for two reasons. First, as a general rule of optimizations, you only
    optimize the things that need it. I think we should wait and measure
    contention and then optimize things. Secondly, we need to get more
    confidence in the correctness of simpler mechanisms in most subsystems
    before we go to something more complex. It will be easier to move to RCU
    once a subsystem is already protected by mutexes.

    I think that this is a good path to go down, but I really don't think
    we're ready yet. I'd rather see energy spent protecting code than
    building more infrastructure.

    Cheers,
    Jeff
    _______________________________________________
    freebsd-arch@freebsd.org mailing list
    http://lists.freebsd.org/mailman/listinfo/freebsd-arch
    To unsubscribe, send any mail to "freebsd-arch-unsubscribe@freebsd.org"

  • Next message: Doug Rabson: "Re: Read Copy Update"