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    SubjectRe: [RFC][PATCH 5/5] perfcounter: Add support for kernel hardware breakpoints
    2009/7/23 Peter Zijlstra <>:
    > On Mon, 2009-07-20 at 13:08 -0400, Frederic Weisbecker wrote:
    >> This adds the support for kernel hardware breakpoints in perfcounter.
    >> It is added as a new type of software counter and can be defined by
    >> using the counter number 5 and by passsing the address of the
    >> breakpoint to set through the config attribute.
    > Is there a limit to these hardware breakpoints? If so, the software
    > counter model is not sufficient, since we assume we can always schedule
    > all software counters. However if you were to add more counters than you
    > have hardware breakpoints you're hosed.

    Hmm, indeed. But this patch handles this case:

    +static const struct pmu *bp_perf_counter_init(struct perf_counter *counter)
    + if (hw_breakpoint_perf_init((unsigned long)counter->attr.config))
    + return NULL;

    IIRC, hw_breakpoint_perf_init() calls register_kernel_breakpoint() which in turn
    returns -ENOSPC if we haven't any breakpoint room left.

    It seems we can only set 4 breakpoints simultaneously in x86, or
    something close to that.

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      Last update: 2009-07-24 16:05    [W:0.025 / U:111.868 seconds]
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