lkml.org 
[lkml]   [2008]   [Jun]   [18]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH][resubmit] x86: enable preemption in delay
    >>> On Wed, Jun 18, 2008 at  8:08 AM, in message <4858C286.BA47.005A.0@novell.com>,
    "Gregory Haskins" <ghaskins@novell.com> wrote:
    >>>> On Wed, Jun 18, 2008 at 3:55 AM, in message <20080618075518.GD4135@elte.hu>,
    > Ingo Molnar <mingo@elte.hu> wrote:
    >
    >> * Marin Mitov <mitov@issp.bas.bg> wrote:
    >>
    >>> Why not something like that (do keep in mind I am not an expert :-):
    >>>
    >>> static void delay_tsc(unsigned long loops)
    >>> {
    >>> get and store the mask of allowed cpus;
    >>> /* prevent the migration */
    >>> set the mask of allowed cpus to the current cpu only;
    >>> /* is it possible? could it be guaranteed? */
    >>> loop for the delay;
    >>> restore the old mask of allowed cpus;
    >>> }
    >>>
    >>> You have got the idea. Could it be realized? Is it more expensive than
    >>> the current realization? So, comments, please.
    >>
    >> hm, changing/saving/restorig cpus_allowed is really considered a 'heavy'
    >> operation compared to preempt_disable(). On a 4096 CPUs box cpus_allowed
    >> is 4096 bits which is half a kilobyte ...
    >>
    >> preempt_disable()/enable() on the other hand only touches a single
    >> variable, (thread_info->preempt_count which is an u32)
    >>
    >> Ingo
    >
    > FWIW: I had submitted some "migration disable" patches a while back that
    > would solve this without the cpus_allowed manipulations described here. Its
    > more expensive than a preempt-disable (but its preemptible), yet its way
    > cheaper (and more correct / less racy) than chaning cpus_allowed. I could
    > resubmit if there was any interest, though I think Ingo said he didnt like
    > the concept on the first pass. Anyway, FYI.

    Sorry, should have provided a reference:

    http://lkml.org/lkml/2008/2/12/344

    >
    > -Greg
    >
    > --
    > To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in
    > the body of a message to majordomo@vger.kernel.org
    > More majordomo info at http://vger.kernel.org/majordomo-info.html




    \
     
     \ /
      Last update: 2008-06-18 14:15    [W:0.023 / U:2.512 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site