Messages in this thread | | | Date | Mon, 25 Apr 2016 13:06:48 -0700 | From | Alexei Starovoitov <> | Subject | Re: [PATCH/RFC v2] perf core: Allow setting up max frame stack depth via sysctl |
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On Mon, Apr 25, 2016 at 04:22:29PM -0300, Arnaldo Carvalho de Melo wrote: > Em Mon, Apr 25, 2016 at 01:27:06PM -0300, Arnaldo Carvalho de Melo escreveu: > > Em Mon, Apr 25, 2016 at 01:14:25PM -0300, Arnaldo Carvalho de Melo escreveu: > > > Em Fri, Apr 22, 2016 at 03:18:08PM -0700, Alexei Starovoitov escreveu: > > > > right... and looking into it further, realized that the patch is broken, > > > > since get_callchain_entry() is doing: > > > > return &entries->cpu_entries[cpu][*rctx]; > > > > whereas it should be dynamic offset based on sysctl_perf_event_max_stack*8 > > > > So definitely needs another respin. > > > struct perf_callchain_entry { > > __u64 nr; > > __u64 ip[0]; /* /proc/sys/kernel/perf_event_max_stack */ > > }; > > > But perf_callchain_entry->ip is not a pointer... Got it ;-\ > > This is what I am building now, a patch on top of the previous, that > will be combined and sent as v3, if I don't find any more funnies: > > diff --git a/kernel/events/callchain.c b/kernel/events/callchain.c > index 6fe77349fa9d..40657892a7e0 100644 > --- a/kernel/events/callchain.c > +++ b/kernel/events/callchain.c > @@ -20,11 +20,10 @@ struct callchain_cpus_entries { > > 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; > -} > +#define __perf_callchain_entry_size(entries) \ > + (sizeof(struct perf_callchain_entry) + sizeof(__u64) * entries) > + > +static size_t perf_callchain_entry_size __read_mostly = __perf_callchain_entry_size(PERF_MAX_STACK_DEPTH); > > static DEFINE_PER_CPU(int, callchain_recursion[PERF_NR_CONTEXTS]); > static atomic_t nr_callchain_events; > @@ -81,7 +80,7 @@ static int alloc_callchain_buffers(void) > if (!entries) > return -ENOMEM; > > - size = perf_callchain_entry__sizeof() * PERF_NR_CONTEXTS; > + size = perf_callchain_entry_size * PERF_NR_CONTEXTS; > > for_each_possible_cpu(cpu) { > entries->cpu_entries[cpu] = kmalloc_node(size, GFP_KERNEL, > @@ -155,7 +154,8 @@ static struct perf_callchain_entry *get_callchain_entry(int *rctx) > > cpu = smp_processor_id(); > > - return &entries->cpu_entries[cpu][*rctx]; > + return (((void *)&entries->cpu_entries[cpu][0]) + > + (*rctx * perf_callchain_entry_size));
I think the following would be easier to read:
+ return (void *)entries->cpu_entries[cpu] + + *rctx * perf_callchain_entry_size; ? if didn't mixed up the ordering...
and probably we could do the math on the spot instead of introducing perf_callchain_entry_size global variable?
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