On Mon, Apr 25, 2016 at 09:29:28PM -0300, Arnaldo Carvalho de Melo wrote: > 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> > Acked-by: David Ahern <dsah...@gmail.com>
Reviewed-by: Frederic Weisbecker <fweis...@gmail.com> I first thought that this should be a tunable per event instead of a global sysctl but then I realized that we still need a root-only-tunable maximum limit value to oppose against any future per event limit and this sysctl value does the job. Nice patch! Thanks.
