Messages in this thread | | | From | Mike Frysinger <> | Date | Fri, 12 Jun 2009 09:21:45 -0400 | Subject | Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported |
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On Fri, Jun 12, 2009 at 09:09, Ingo Molnar wrote: > * Mike Frysinger <vapier.adi@gmail.com> wrote: >> On Fri, Jun 12, 2009 at 08:59, Ingo Molnar wrote: >> > * Mike Frysinger <vapier.adi@gmail.com> wrote: >> >> On Fri, Jun 12, 2009 at 08:31, Ingo Molnar wrote: >> >> > * Mike Frysinger <vapier.adi@gmail.com> wrote: >> >> >> On Fri, Jun 12, 2009 at 08:17, Ingo Molnar wrote: >> >> >> > * 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. >> >> >> >> >> >> >> >> if there is generic support available, why must every arch select >> >> >> >> HAVE_PERF_COUNTERS in their Kconfig ? >> >> >> > >> >> >> > Because we only want to enable it on architectures that have tested >> >> >> > it. It should only need a syscall addition, but nothing beats having >> >> >> > tested things, hence we have that additional Kconfig symbol. >> >> >> >> >> >> that is a pretty weak reason. [...] >> >> > >> >> > It isnt - this is proper isolation - dont offer something to the >> >> > user to enable that 1) cannot be used due to the lack of a syscall >> >> > 2) has not been tested by anyone on that architecture, ever. >> >> > >> >> > That way say build breakages or runtime failures due to perfcounters >> >> > only become possible on an architecture if the architecture >> >> > maintainer has hooked up the syscall and has provided >> >> > HAVE_PERF_COUNTERS explicitly. >> >> >> >> except that the syscall presence is trivial to detect in the code by >> >> something like: >> >> #ifndef __NR_perf_counter_open >> >> # error sorry, your arch has not hooked up perf_counter_open syscall yet >> >> #endif >> >> >> >> as for "no arch testing yet", there are plenty of drivers which lack >> >> arch depends in the Kconfig specifically so that it can be *easily* >> >> tested on random systems out there without requiring manual twiddling. >> > >> > This is a new kernel subsystem, not just yet another driver. >> >> so what ? if it has generic pieces, it is exactly the same as yet >> another generic driver. people should be able to randomly test >> build it when possible to discover latent issues that your testing >> limited to one arch did not find. >> >> > Which bit of: "we dont want perfcounters to be enabled in the >> > Kconfig on architectures that have no syscalls and no testing for >> > it" is hard to understand? It is a valid technical concern. >> >> your (1) is valid but i already pointed out a simple fix for that. >> your (2) is not. > > Uhm, your 'fix': > > #ifndef __NR_perf_counter_open > # error sorry, your arch has not hooked up perf_counter_open syscall yet > #endif > > is completely unacceptable. We dont propagate build failures via > user-enable config options, we never did. There's a lot of people > doing randconfig builds - if it randomly failed due to your 'fix' > that would upset a lot of testing for no good reason.
accept that is a valid bug: the arch is missing the syscall and it should hook it up -mike -- 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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