lkml.org 
[lkml]   [2010]   [Nov]   [25]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 1/3] jump label: add enabled/disabled state to jump label key entries
    * Peter Zijlstra (peterz@infradead.org) wrote:
    [...]
    > > What would suit us would be to have an arch callback that is called
    > > after all the transforms for a particular jump label key have been made.
    > > That way we could optimise the individual patches, and do a sync step at
    > > the end, ie. when we want the effect of the patching to be globally
    > > visible.
    >
    > I think such a sync-barrier is desired (possibly only on the enable
    > path) so we can actually say the tracepoints are on.
    >
    > Which would mean sending IPIs to all CPUs and waiting for them to
    > acknowledge them. Which, while not quite as expensive as stop_machine,
    > its not really cheap either.

    Yep, although this can be batched when enabling many tracepoints en
    masse. May I suggest that you guys benchmark the two approaches so we
    can figure out at how many tracepoints we start hitting a latency wall ?
    100, 1000 and 10000 tracepoints should give interesting measurement
    points. If we are still below 2 seconds on common hardware when enabling
    10000 tracepoints, then the binary search might be fine.

    Please note that HPA recommended the use of a perfect hash. It would
    make sense, although there seems to be a non-null probability that the
    perfect hash cannot be generated. There are techniques that will retry
    with a different seed, but the kernel build time then becomes slightly
    harder to predict (for very, very rare occurences, so maybe we don't
    care).

    Thanks,

    Mathieu

    --
    Mathieu Desnoyers
    Operating System Efficiency R&D Consultant
    EfficiOS Inc.
    http://www.efficios.com


    \
     
     \ /
      Last update: 2010-11-25 15:03    [W:2.730 / U:1.020 seconds]
    ©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site