Messages in this thread Patch in this message | | | Date | Fri, 12 Jan 2018 11:20:32 -0300 | From | Arnaldo Carvalho de Melo <> | Subject | Re: [PATCH v2] perf trace: Fix missing handling of --call-graph dwarf |
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Em Fri, Jan 12, 2018 at 11:03:55AM +0100, Thomas Richter escreveu: > 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.
It is global, but then, per-event settings can override it.
So if you say that the following call (without that /max-stack=3/, which implies DWARF, which is the safest bet for userspace callchains): [root@jouet ~]# perf trace --no-syscalls --call-graph dwarf -e probe_libc:inet_pton ping -6 -c 1 ::1 PING ::1(::1) 56 data bytes 64 bytes from ::1: icmp_seq=1 ttl=64 time=0.086 ms
--- ::1 ping statistics --- 1 packets transmitted, 1 received, 0% packet loss, time 0ms rtt min/avg/max/mdev = 0.086/0.086/0.086/0.000 ms 0.000 probe_libc:inet_pton:(7fafee7ce350)) [root@jouet ~]#
And it doesn't work, right, that is a bug. I'll check if your patch fixes that and then will correct the cset log, i.e. this part:
[root@f27 perf]# ./perf trace --no-syscalls --call-graph dwarf -e probe_libc:inet_pton/max-stack=3/ ping -6 -c 1 ::1
Should read:
[root@f27 perf]# ./perf trace --no-syscalls --call-graph dwarf -e probe_libc:inet_pton ping -6 -c 1 ::1
And _should_ produce a call-graph, without a stack limit, ok?
I'll reply to this message after testing your patch.
Thanks,
- Arnaldo
> 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 <tmricht@linux.vnet.ibm.com> > Reviewed-by: Hendrick Brueckner <brueckner@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
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