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Subject[PATCH] perf/report: [RFC] Handling OOM in perf report
Date
A very strange -ENOMEM error which only when output
is displayed using the GTK GUI (I have copied the text from the GUI):

[root@m35lp76 perf]# ./perf report -i perf.data.error68-1

Processing events... [974K/3M]
Error:failed to process sample

0xf4198 [0x8]: failed to process type: 68

However when I use the same perf.data file with --stdio it works:

[root@m35lp76 perf]# ./perf report -i perf.data.error68-1 --stdio \
| head -12

# Total Lost Samples: 0
#
# Samples: 76K of event 'cycles'
# Event count (approx.): 99056160000
#
# Overhead Command Shared Object Symbol
# ........ ............... ................. .........
#
8.81% find [kernel.kallsyms] [k] ftrace_likely_update
8.74% swapper [kernel.kallsyms] [k] ftrace_likely_update
8.34% sshd [kernel.kallsyms] [k] ftrace_likely_update
2.19% kworker/u512:1- [kernel.kallsyms] [k] ftrace_likely_update

The sample precentage is a bit low.....

It always fails in the FINISHED_ROUND event, event number 68.

When happened is the following. Perf report calls a lot of functions and
down deep when a FINISHED_ROUND event is processed, these functions are
called:

perf_session__process_event()
+ perf_session__process_user_event()
+ process_finished_round()
+ ordered_events__flush()
+ __ordered_events__flush()
+ do_flush()
+ ordered_events__deliver_event()
+ perf_session__deliver_event()
+ machine__deliver_event()
+ perf_evlist__deliver_event()
+ process_sample_event()
+ hist_entry_iter_add() --> only called in GUI case!!!
+ hist_iter__report__callback()
+ symbol__inc_addr_sample()

Now this functions runs out of memory and
returns -ENOMEM. This is reported all the way up
until function

perf_session__process_event() returns to its caller, where -ENOMEM is
changed to -EINVAL and processing stops:

if ((skip = perf_session__process_event(session, event, head)) < 0) {
pr_err("%#" PRIx64 " [%#x]: failed to process type: %d\n",
head, event->header.size, event->header.type);
err = -EINVAL;
goto out_err;
}

This occured in the FINISHED_ROUND event when it has to process some
10000 entries and ran out of memory.

I understand that my perf.data file might just be too big, but I would
like to see some error message indicating OOM error instead of
processing failure of a unrelated event.

However this patch just does what the pr_debug() statement indicates,
the event is skipped and processing continues.
But at least the root cause is indicated and also shows up in the
GUI.

Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
---
tools/perf/builtin-report.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
index 4054eb1f98ac..7a27b815f7a8 100644
--- a/tools/perf/builtin-report.c
+++ b/tools/perf/builtin-report.c
@@ -283,8 +283,13 @@ static int process_sample_event(struct perf_tool *tool,
al.map->dso->hit = 1;

ret = hist_entry_iter__add(&iter, &al, rep->max_stack, rep);
- if (ret < 0)
+ if (ret < 0) {
pr_debug("problem adding hist entry, skipping event\n");
+ if (ret == -ENOMEM) {
+ pr_err("Running out of memory\n");
+ ret = 0;
+ }
+ }
out_put:
addr_location__put(&al);
return ret;
--
2.16.4
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