[lkml]   [2010]   [Aug]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
    SubjectRe: A question of perf NMI handler
    On 04.08.10 05:21:10, Lin Ming wrote:

    > With nmi_watchdog enabled, perf_event_nmi_handler always return
    > NOTIFY_STOP(active_events > 0), and the notifier call chain will not
    > call further.
    > If it was not perf NMI, does the perf nmi handler may stop the real NMI
    > handler get called because NOTIFY_STOP is returned??

    There is no general mechanism for recording the NMI source (except if
    it was external triggered, e.g. by the southbridge). Also, all nmis
    are mapped to NMI vector 2 and therefore there is no way to find out
    the reason by using apic mask registers.

    Now, if multiple perfctrs trigger an nmi, it may happen that a handler
    has nothing to do because the counter was already handled by the
    previous one. Thus, it is valid to have unhandled nmis caused by

    So, with counters enabled we always have to return stop for *all* nmis
    as we cannot detect that it was an perfctr nmi. Otherwise we could
    trigger an unhandled nmi. To ensure that all other nmi handlers are
    called, the perfctr's nmi handler must have the lowest priority. Then,
    the handler will be the last in the chain.


    Advanced Micro Devices, Inc.
    Operating System Research Center

     \ /
      Last update: 2010-08-04 12:07    [W:0.022 / U:25.432 seconds]
    ©2003-2017 Jasper Spaans. hosted at Digital OceanAdvertise on this site