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perf: Return empty callchain instead of NULL

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It simplifies the code a bit, because we dump the callchain
Link: http://lkml.kernel.org/n/tip-uqp7qd6aif47g39glnbu95yl@git.kernel.org
even if it's empty. With 'empty' callchain we can remove
all the NULL-checking code paths.

Original-patch-from: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: http://lkml.kernel.org/r/20180107160356.28203-7-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
This commit is contained in:
Jiri Olsa 2018-01-07 17:03:50 +01:00 committed by Arnaldo Carvalho de Melo
parent 8cf7e0e224
commit 99e818cc88
1 changed files with 12 additions and 18 deletions
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30
kernel/events/core.c
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@ -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;
int size = 1;
if (data->callchain)
size += data->callchain->nr;
size *= sizeof(u64);
__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);
}