lkml.org 
[lkml]   [2006]   [Nov]   [3]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: New filesystem for Linux
    On Thu, Nov 02, 2006 at 03:15:33PM -0800, Linus Torvalds wrote:
    >
    >
    > On Thu, 2 Nov 2006, Mikulas Patocka wrote:
    > >
    > > * There is a rw semaphore that is locked for read for nearly all operations
    > > and locked for write only rarely. However locking for read causes cache line
    > > pingpong on SMP systems. Do you have an idea how to make it better?

    [ . . . ]

    > (Seqlocks could be changed to drop the first requirement, although it
    > could cause some serious starvation issues, so I'm not sure it's a good
    > idea. For RCU the atomic nature is pretty much designed-in.)

    I can't help putting in a plug for SRCU, which is in the 2.6.19-rc series,
    and which allows readers to sleep. (http://lwn.net/Articles/202847/)

    SRCU allows readers and writers to run concurrently (as do all forms of
    RCU). If this is a problem, it might be worth looking into Gautham
    Shenoy's reader-writer lock built on top of RCU. (A version for hotplug
    may be found at http://lkml.org/lkml/2006/10/26/73.) This approach
    keeps the reader-writer-lock semantics, but gets rid of cache thrashing.
    That said, writers have to wait for a grace period.

    And as Linus pointed out, if you have disk I/O involved, you probably
    won't notice normal reader-writer-lock overhead.

    Thanx, Paul
    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-11-03 21:03    [W:4.240 / U:0.144 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site