lkml.org 
[lkml]   [2007]   [Oct]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [patch 2/2] cpusets: add interleave_over_allowed option
    On Thu, 25 Oct 2007, David Rientjes wrote:

    > The problem occurs when you add cpusets into the mix and permit the
    > allowed nodes to change without knowledge to the application. Right now,
    > a simple remap is done so if the cardinality of the set of nodes
    > decreases, you're interleaving over a smaller number of nodes. If the
    > cardinality increases, your interleaved nodemask isn't expanded. That's
    > the problem that we're facing. The remap itself is troublesome because it
    > doesn't take into account the user's desire for a custom nodemask to be
    > used anyway; it could remap an interleaved policy over several nodes that
    > will already be contended with one another.

    Right. So I think we are fine if the application cannot setup boundaries
    for interleave.


    > Normally, MPOL_INTERLEAVE is used to reduce bus contention to improve the
    > throughput of the application. If you remap the number of nodes to
    > interleave over, which is currently how it's done when mems_allowed
    > changes, you could actually be increasing latency because you're
    > interleaving over the same bus.

    Well you may hit some nodes more than others so a slight performance
    degradataion.

    > This isn't a memory policy problem because all it does is effect a
    > specific policy over a set of nodes. With my change, cpusets are required
    > to update the interleaved nodemask if the user specified that they desire
    > the feature with interleave_over_allowed. Cpusets are, after all, the
    > ones that changed the mems_allowed in the first place and invalidated our
    > custom interleave policy. We simply can't make inferences about what we
    > should do, so we allow the creator of the cpuset to specify it for us. So
    > the proper place to modify an interleaved policy is in cpusets and not
    > mempolicy itself.

    With that MPOL_INTERLEAVE would be context dependent and no longer
    needs translation. Lee had similar ideas. Lee: Could we make
    MPOL_INTERLEAVE generally cpuset context dependent?

    -
    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: 2007-10-26 02:31    [W:4.348 / U:0.664 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site