Em Tue, Apr 26, 2016 at 11:58:10PM +0200, Frederic Weisbecker escreveu: > 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
Yeah, I'll work on that too. > 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 for reviewieng it! - Arnaldo
