On Mon, Apr 25, 2016 at 09:29:28PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Mon, Apr 25, 2016 at 05:07:26PM -0700, Alexei Starovoitov escreveu:
> > > + {
> > > + .procname = "perf_event_max_stack",
> > > + .data = NULL, /* filled in by handler */
> > > + .maxlen = sizeof(sysctl_perf_event_max_stack),
> > > + .mode = 0644,
> > > + .proc_handler = perf_event_max_stack_handler,
> > > + .extra1 = &zero,
> > > + },
>
> > you need to define a max value otherwise perf_callchain_entry__sizeof
> > will overflow. Sure it's root only facility, but still not nice.
> > 1M? Anything above 1M stack frames would be insane anyway.
> > The rest looks good. Thanks!
>
> Something else? ;-)
all looks good to me. Thanks a bunch!
>
> commit cd544af4f7fede01cb512d52bb3efe62aa19271d
> Author: Arnaldo Carvalho de Melo <a...@redhat.com>
> Date: Thu Apr 21 12:28:50 2016 -0300
>
> perf core: Allow setting up max frame stack depth via sysctl
>
> The default remains 127, which is good for most cases, and not even hit
> most of the time, but then for some cases, as reported by Brendan, 1024+
> deep frames are appearing on the radar for things like groovy, ruby.
>
> And in some workloads putting a _lower_ cap on this may make sense. One
> that is per event still needs to be put in place tho.
>
> The new file is:
>
> # cat /proc/sys/kernel/perf_event_max_stack
> 127
>
> Chaging it:
>
> # echo 256 > /proc/sys/kernel/perf_event_max_stack
> # cat /proc/sys/kernel/perf_event_max_stack
> 256
>
> But as soon as there is some event using callchains we get:
>
> # echo 512 > /proc/sys/kernel/perf_event_max_stack
> -bash: echo: write error: Device or resource busy
> #
>
> Because we only allocate the callchain percpu data structures when there
> is a user, which allows for changing the max easily, its just a matter
> of having no callchain users at that point.
>
> Reported-and-Tested-by: Brendan Gregg <brendan.d.gr...@gmail.com>
> Acked-by: Alexei Starovoitov <a...@kernel.org>
yep :)
hopefully Brendan can give it another spin.
