Messages in this thread | | | Date | Fri, 12 Jun 2009 18:57:16 +0200 | From | Ingo Molnar <> | Subject | Re: [PATCH] scripts/checksyscalls.sh: only whine perf_counter_open when supported |
| |
* Ingo Molnar <mingo@elte.hu> wrote:
> > * Mike Frysinger <vapier.adi@gmail.com> wrote: > > > 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 > > Uhm, that's ridiculous, observe lkml for a few weeks and see what > happens when any subsystem fails to build in a user-configurable > variation. Even if it's "just" because something like a syscall > definition is missing. > > Anyway, i have no time to teach you about kernel mainteinance > basics really so i probably wont follow up on future emails.
Mike, i'd like to apologize for the tone of this reply - it was certainly over the top, especially considering the fact that you were right with your original patch :)
Merge window stress is not making me particularly patient i guess :-/
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/
| |