Messages in this thread | | | Date | Thu, 21 Apr 2016 12:48:58 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH/RFC] perf core: Allow setting up max frame stack depth via sysctl |
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On Wed, Apr 20, 2016 at 07:47:30PM -0300, Arnaldo Carvalho de Melo wrote: > 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.
yea gawds ;-)
> index 343c22f5e867..1390747b2195 100644 > --- a/kernel/events/callchain.c > +++ b/kernel/events/callchain.c > @@ -18,6 +18,14 @@ struct callchain_cpus_entries { > struct perf_callchain_entry *cpu_entries[0]; > }; > > +int sysctl_perf_event_max_stack __read_mostly = PERF_MAX_STACK_DEPTH; > + > +static size_t perf_callchain_entry__sizeof(void) > +{ > + return sizeof(struct perf_callchain_entry) + > + sizeof(__u64) * sysctl_perf_event_max_stack; > +} > + > static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]); > static atomic_t nr_callchain_events; > static DEFINE_MUTEX(callchain_mutex); > @@ -73,7 +81,7 @@ static int alloc_callchain_buffers(void) > if (!entries) > return -ENOMEM; > > - size = sizeof(struct perf_callchain_entry) * PERF_NR_CONTEXTS; > + size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS; > > for_each_possible_cpu(cpu) { > entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL,
And this alloc _will_ fail if you put in a decent sized value..
Should we put in a dmesg WARN if this alloc fails and perf_event_max_stack is 'large' ?
> @@ -215,3 +223,25 @@ exit_put: > > return entry; > } > + > +int perf_event_max_stack_handler(struct ctl_table *table, int write, > + void __user *buffer, size_t *lenp, loff_t *ppos) > +{ > + int new_value = sysctl_perf_event_max_stack, ret; > + struct ctl_table new_table = *table; > + > + new_table.data = &new_value;
cute :-)
> + ret = proc_dointvec_minmax(&new_table, write, buffer, lenp, ppos); > + if (ret || !write) > + return ret; > + > + mutex_lock(&callchain_mutex); > + if (atomic_read(&nr_callchain_events)) > + ret = -EBUSY; > + else > + sysctl_perf_event_max_stack = new_value; > + > + mutex_unlock(&callchain_mutex); > + > + return ret; > +}
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