1. 13 2月, 2015 1 次提交
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      perf: Decouple unthrottling and rotating · 2fde4f94
      Mark Rutland 提交于
      Currently the adjusments made as part of perf_event_task_tick() use the
      percpu rotation lists to iterate over any active PMU contexts, but these
      are not used by the context rotation code, having been replaced by
      separate (per-context) hrtimer callbacks. However, some manipulation of
      the rotation lists (i.e. removal of contexts) has remained in
      perf_rotate_context(). This leads to the following issues:
      
      * Contexts are not always removed from the rotation lists. Removal of
        PMUs which have been placed in rotation lists, but have not been
        removed by a hrtimer callback can result in corruption of the rotation
        lists (when memory backing the context is freed).
      
        This has been observed to result in hangs when PMU drivers built as
        modules are inserted and removed around the creation of events for
        said PMUs.
      
      * Contexts which do not require rotation may be removed from the
        rotation lists as a result of a hrtimer, and will not be considered by
        the unthrottling code in perf_event_task_tick.
      
      This patch fixes the issue by updating the rotation ist when events are
      scheduled in/out, ensuring that each rotation list stays in sync with
      the HW state. As each event holds a refcount on the module of its PMU,
      this ensures that when a PMU module is unloaded none of its CPU contexts
      can be in a rotation list. By maintaining a list of perf_event_contexts
      rather than perf_event_cpu_contexts, we don't need separate paths to
      handle the cpu and task contexts, which also makes the code a little
      simpler.
      
      As the rotation_list variables are not used for rotation, these are
      renamed to active_ctx_list, which better matches their current function.
      perf_pmu_rotate_{start,stop} are renamed to
      perf_pmu_ctx_{activate,deactivate}.
      Reported-by: NJohannes Jensen <johannes.jensen@arm.com>
      Signed-off-by: NMark Rutland <mark.rutland@arm.com>
      Signed-off-by: NPeter Zijlstra (Intel) <peterz@infradead.org>
      Cc: Will Deacon <Will.Deacon@arm.com>
      Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
      Cc: Fengguang Wu <fengguang.wu@intel.com>
      Cc: Linus Torvalds <torvalds@linux-foundation.org>
      Link: http://lkml.kernel.org/r/20150129134511.GR17721@leverpostejSigned-off-by: NIngo Molnar <mingo@kernel.org>
      2fde4f94