Messages in this thread | | | Date | Fri, 12 Jun 2009 17:21:34 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported |
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* 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 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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