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    SubjectRe: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported

    * Mike Frysinger <vapier.adi@gmail.com> wrote:

    > On Fri, Jun 12, 2009 at 08:05, Ingo Molnar wrote:
    > > * Mike Frysinger <vapier@gentoo.org> wrote:
    > >> If the port does not support HAVE_PERF_COUNTERS, then they can't
    > >> support the perf_counter_open syscall either.  Rather than forcing
    > >> everyone to add an ignore (or suffer the warning until they get
    > >> around to implementing support), only whine about the syscall when
    > >> applicable.
    > >
    > > No, this patch is wrong - it's really easy to add support: just hook
    > > up the syscall. This should happen for every architecture really, so
    > > the warning is correct and it should not be patched out.
    > >
    > > PMU support is not required to get perfcounters support: if an
    > > architecture hooks up the syscall it will get generic software
    > > counters and the tools will work as well.
    > >
    > > Profiling falls back to a hrtimer-based sampling method - this is a
    > > much better fallback than oprofile's fall-back to the timer tick.
    > > This hrtimer based sampling is dynticks/nohz-correct and can go
    > > beyond HZ if the architecture supports hrtimers.
    >
    > these statements are actually incorrect. the perf counter code
    > explicitly requires:
    > - asm/perf_counter.h

    An empty stub suffices.

    > - support for atomic64 types (unless i missed something, x86 is the
    > only 32bit system that supports these)

    A wrapper suffices - should probably be librarized into lib/.

    > - some perf stubs (like set_perf_counter_pending() -- prototype
    > really should be in common perf_counters headers rather than forcing
    > the arch to copy & paste the exact same line)

    Agreed.

    > not that any of this is documented ...

    Patches are welcome :-)

    You are right that the requirements are not necessarily trivial for
    every arch - so i guess our original patch is correct.

    Acked-by: Ingo Molnar <mingo@elte.hu>

    Ingo
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