On Intel platform when I execute test case
probe libc's inet_pton & backtrace it with ping
I get this output which is correct:
[root@f27 perf]# ./perf trace --no-syscalls
-e probe_libc:inet_pton/max-stack=3/ ping -6 -c 1 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.064 ms
--- ::1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.064/0.064/0.064/0.000 ms
0.000 probe_libc:inet_pton:(7f26a88498a0))
__GI___inet_pton (/usr/lib64/libc-2.26.so)
getaddrinfo (/usr/lib64/libc-2.26.so)
main (/usr/bin/ping)
[root@f27 perf]#
However when I add the global --call-graph dwarf to the command
line I get the exactly same result which is wrong:
[root@f27 perf]# ./perf trace --no-syscalls --call-graph dwarf
-e probe_libc:inet_pton/max-stack=3/ ping -6 -c 1 ::1
My understanding is that the '--call-graph dwarf' option should be global
and applies to all events. However it is ignored.
The issue is buried in function apply_config_terms() called from
trace__run()
--> perf_evlist__config()
--> perf_evsel__config()
--> apply_config_terms()
This function iterates over all additional terms and handles the
/max-stack=<xx>/ case. However if there is no additional call-graph=dwarf
setting as in -e probe_libc:inet_pton/max-stack=3,call-graph=dwarf/
the function defaults to "fp" regardless of the value of --call-graph
global command line flag.
So when I add ,call-graph=dwarf to the event I get a good result:
[root@f27 perf]# ./perf trace --no-syscalls
-e probe_libc:inet_pton/max-stack=3,call-graph=dwarf/
ping -6 -c 1 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.084 ms
--- ::1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.084/0.084/0.084/0.000 ms
0.000 probe_libc:inet_pton:(7f9372a988a0))
__inet_pton (inlined)
gaih_inet.constprop.7 (/usr/lib64/libc-2.26.so)
__GI_getaddrinfo (inlined)
main (/usr/bin/ping)
__libc_start_main (/usr/lib64/libc-2.26.so)
_start (/usr/bin/ping)
[root@f27 perf]#
In fact the looks pretty similar to the output on s390x which only has
dwarf support.
Ok the max-stack is not observed, but this time the global --max-stack <x>
comes to rescue and limits the output:
[root@f27 perf]# ./perf trace --no-syscalls --max-stack 4
-e probe_libc:inet_pton/max-stack=3,call-graph=dwarf/ ping -6 -c 1 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.061 ms
--- ::1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.061/0.061/0.061/0.000 ms
0.000 probe_libc:inet_pton:(7fc9f6c188a0))
__inet_pton (inlined)
gaih_inet.constprop.7 (/usr/lib64/libc-2.26.so)
__GI_getaddrinfo (inlined)
main (/usr/bin/ping)
[root@f27 perf]#
This patch applies the global --call-graph <xxx> setting to the individual
events.
With this patch applied:
[root@f27 perf]# ./perf trace --no-syscalls --call-graph dwarf
-e probe_libc:inet_pton/max-stack=3/ ping -6 -c 1 ::1
PING ::1(::1) 56 data bytes
64 bytes from ::1: icmp_seq=1 ttl=64 time=0.066 ms
--- ::1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.066/0.066/0.066/0.000 ms
0.000 probe_libc:inet_pton:(7fe74f8358a0))
__inet_pton (inlined)
gaih_inet.constprop.7 (/usr/lib64/libc-2.26.so)
__GI_getaddrinfo (inlined)
main (/usr/bin/ping)
__libc_start_main (/usr/lib64/libc-2.26.so)
_start (/usr/bin/ping)
[root@f27 perf]#
When using dwarf the /max-stack=<x>/ is not observed.
The reason is that for call-graph=fp the kernel stack unwinder
is used and it stops after unwinding x entries.
For dwarf the complete stack data is returned and the unwinding
is done by perf itself and it uses --max-stack <x>
command line flag.
Signed-off-by: Thomas Richter <tmri...@linux.vnet.ibm.com>
Reviewed-by: Hendrick Brueckner <brueck...@linux.vnet.ibm.com>
---
tools/perf/util/evsel.c | 20 ++++++++++++++++++--
1 file changed, 18 insertions(+), 2 deletions(-)
diff --git a/tools/perf/util/evsel.c b/tools/perf/util/evsel.c
index d5fbcf8c7aa7..d1c25aafb821 100644
--- a/tools/perf/util/evsel.c
+++ b/tools/perf/util/evsel.c
@@ -788,8 +788,24 @@ static void apply_config_terms(struct perf_evsel *evsel,
if ((callgraph_buf != NULL) || (dump_size > 0) || max_stack) {
if (max_stack) {
param.max_stack = max_stack;
- if (callgraph_buf == NULL)
- callgraph_buf = "fp";
+ if (callgraph_buf == NULL) {
+ switch (callchain_param.record_mode) {
+ case CALLCHAIN_DWARF:
+ callgraph_buf = "dwarf";
+ break;
+ case CALLCHAIN_NONE:
+ case CALLCHAIN_FP:
+ callgraph_buf = "fp";
+ break;
+ case CALLCHAIN_LBR:
+ callgraph_buf = "lbr";
+ break;
+ default:
+ case CALLCHAIN_MAX:
+ callgraph_buf = "no";
+ break;
+ }
+ }
}
/* parse callgraph parameters */
--
2.14.3
