lkml.org 
[lkml]   [2001]   [Sep]   [21]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    From
    Date
    SubjectRe: [reiserfs-list] Re: [PATCH] Significant performace improvements on reiserfs systems
    Andrew Morton writes:
    > george anzinger wrote:
    > >
    > > ...
    > > Actually, I rather think that the problem is lock granularity. These
    > > issues are present in the SMP systems as well. A good solution would be
    > > one that shortened the spinlock time. No horrid preempt code, just
    > > tight fast code.
    > >
    >
    > This may not be practical.
    >
    > Take, for example, zap_page_range(). It simply has a lot
    > of work to do, and it does it inside a spinlock. By doing
    > it in a tight loop, it's optimal.
    >
    > There is no way to speed this function up by two or three orders
    > of magnitude. (Well, there is: don't take the lock at all if
    > the mm isn't shared, but this is merely an example. There are
    > other instances).
    >
    > It seems that for a preemptive kernel to be successful, we need
    > to globally alter the kernel so that it never holds locks for
    > more than 500 microseconds. Which is what the conditional_schedule()
    > (aka cooperative multitasking :)) patches do.
    >
    > It seems that there are no magic bullets, and low latency will
    > forever have a global impact on kernel design, unless a way is
    > found to reschedule with locks held. I recall that a large

    In Solaris, before spinning on a busy spin-lock, thread checks whether
    spin-lock holder runs on the same processor. If so, thread goes to sleep
    and holder wakes it up on spin-lock release. The same, I guess is going
    for interrupts that are served as separate threads. This way, one can
    re-schedule with spin-locks held.

    > part of the MontaVista patch involved turning spinlocks into
    > semaphores, yes? That would seem to be the way to go.

    Nikita.
    -
    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: 2005-03-22 13:03    [W:2.563 / U:0.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site