On Sun, Jan 07, 2018 at 05:03:50PM +0100, Jiri Olsa wrote: > It simplifies the code a bit, because we dump the callchain > even if it's empty. With 'empty' callchain we can remove > all the NULL-checking code paths.
Acked-by: Peter Zijlstra (Intel) <pet...@infradead.org> > > Original-patch-from: Peter Zijlstra <pet...@infradead.org> > Link: http://lkml.kernel.org/n/tip-n4t869o2qc1b31v4wwvmx...@git.kernel.org > Signed-off-by: Jiri Olsa <jo...@kernel.org> > --- > kernel/events/core.c | 30 ++++++++++++------------------ > 1 file changed, 12 insertions(+), 18 deletions(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 5fc1ded4b450..4e1a1bf8d867 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -5815,19 +5815,11 @@ void perf_output_sample(struct perf_output_handle > *handle, > perf_output_read(handle, event); > > if (sample_type & PERF_SAMPLE_CALLCHAIN) { > - if (data->callchain) { > - int size = 1; > - > - if (data->callchain) > - size += data->callchain->nr; > - > - size *= sizeof(u64); > + int size = 1; > > - __output_copy(handle, data->callchain, size); > - } else { > - u64 nr = 0; > - perf_output_put(handle, nr); > - } > + size += data->callchain->nr; > + size *= sizeof(u64); > + __output_copy(handle, data->callchain, size); > } > > if (sample_type & PERF_SAMPLE_RAW) { > @@ -5980,6 +5972,8 @@ static u64 perf_virt_to_phys(u64 virt) > return phys_addr; > } > > +static struct perf_callchain_entry __empty_callchain = { .nr = 0, }; > + > static struct perf_callchain_entry * > perf_callchain(struct perf_event *event, struct pt_regs *regs) > { > @@ -5988,12 +5982,14 @@ perf_callchain(struct perf_event *event, struct > pt_regs *regs) > /* Disallow cross-task user callchains. */ > bool crosstask = event->ctx->task && event->ctx->task != current; > const u32 max_stack = event->attr.sample_max_stack; > + struct perf_callchain_entry *callchain; > > if (!kernel && !user) > - return NULL; > + return &__empty_callchain; > > - return get_perf_callchain(regs, 0, kernel, user, > - max_stack, crosstask, true); > + callchain = get_perf_callchain(regs, 0, kernel, user, > + max_stack, crosstask, true); > + return callchain ?: &__empty_callchain; > } > > void perf_prepare_sample(struct perf_event_header *header, > @@ -6018,9 +6014,7 @@ void perf_prepare_sample(struct perf_event_header > *header, > int size = 1; > > data->callchain = perf_callchain(event, regs); > - > - if (data->callchain) > - size += data->callchain->nr; > + size += data->callchain->nr; > > header->size += size * sizeof(u64); > } > -- > 2.13.6 >
