On 03/21/2017 11:21 PM, Arnaldo Carvalho de Melo wrote:
Em Tue, Mar 21, 2017 at 11:14:07AM -0300, Arnaldo Carvalho de Melo escreveu:
Em Tue, Mar 21, 2017 at 07:20:20AM +0900, Taeung Song escreveu:
And,
I tested by perf-stat on the same situation as below.
$ perf stat -e "{cycles,page-faults,branch-misses}" ./old <input.txt
6623856
Please always try to spell out all the steps needed to get to some
result, for instance, in this case the info above, that you are asking
for three counters to be recorded at once probably has the key to
reproduce this, as I think that you may run your workload and sometimes
not get one page fault, leading tho that division by zero, but I have to
try to reproduce it now that I have this clue.
Bingo!
[root@jouet ~]# perf record -e "{cycles,page-faults,branch-misses}" usleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.020 MB perf.data (20 samples) ]
[root@jouet ~]# perf annotate -l --stdio 2>&1 | grep -w nan | head
100.00 -nan 100.00 msr.h:104
0.00 -nan 0.00 : ffffffff81060bf0: mov %edi,%ecx
0.00 -nan 0.00 : ffffffff81060bf2: mov %esi,%eax
0.00 -nan 0.00 : ffffffff81060bf4: wrmsr
msr.h:104 100.00 -nan 100.00 : ffffffff81060bf6: nopl
0x0(%rax,%rax,1)
0.00 -nan 0.00 : ffffffff81060bfb: retq
0.00 -nan 0.00 : ffffffff81060bfc: push %rbp
0.00 -nan 0.00 : ffffffff81060bfd: mov %esi,%eax
0.00 -nan 0.00 : ffffffff81060bff: mov %rdx,%rsi
0.00 -nan 0.00 : ffffffff81060c02: shl $0x20,%rsi
[root@jouet ~]#
So, if we don't use -l/--print-line we get:
[root@jouet ~]# perf annotate --stdio --no-source native_write_msr
Percent | Source code & Disassembly of vmlinux for cycles
(3 samples)
-------------------------------------------------------------------------------------------
: ffffffff81060bf0 <native_write_msr>:
: __wrmsr():
0.00 0.00 0.00 : ffffffff81060bf0: mov %edi,%ecx
0.00 0.00 0.00 : ffffffff81060bf2: mov %esi,%eax
0.00 0.00 0.00 : ffffffff81060bf4: wrmsr
: arch_static_branch():
100.00 0.00 100.00 : ffffffff81060bf6: nopl
0x0(%rax,%rax,1)
: native_write_msr():
0.00 0.00 0.00 : ffffffff81060bfb: retq
0.00 0.00 0.00 : ffffffff81060bfc: push %rbp
0.00 0.00 0.00 : ffffffff81060bfd: mov %esi,%eax
0.00 0.00 0.00 : ffffffff81060bff: mov %rdx,%rsi
0.00 0.00 0.00 : ffffffff81060c02: shl $0x20,%rsi
0.00 0.00 0.00 : ffffffff81060c06: mov %eax,%edx
0.00 0.00 0.00 : ffffffff81060c08: mov %rsp,%rbp
0.00 0.00 0.00 : ffffffff81060c0b: or %rdx,%rsi
0.00 0.00 0.00 : ffffffff81060c0e: xor %edx,%edx
0.00 0.00 0.00 : ffffffff81060c10: callq ffffffff81457df0
<do_trace_write_msr>
0.00 0.00 0.00 : ffffffff81060c15: pop %rbp
0.00 0.00 0.00 : ffffffff81060c16: retq
[root@jouet ~]#
I.e. one column per event in that group, and no -nan, all is well.
The reason is the below if statement at util/annotate.c:910.
881 double disasm__calc_percent(struct annotation *notes, int evidx, s64
offset,
...
904 struct sym_hist *h = annotation__histogram(notes,
evidx);
905 unsigned int hits = 0;
906
907 while (offset < end)
908 hits += h->addr[offset++];
909
910 if (h->sum) {
911 *nr_samples = hits;
912 percent = 100.0 * hits / h->sum;
913 }
914 }
The if statement 'if (h->sum)' prevent division by zero, so all is well.
So I sent this patch because of same reason
adding the if statement 'if (h->sum)' in symbol__get_source_line().
But will resend v2 with more clearly commit log message!
I think previous log message is a bit insufficient..
Thanks,
Taeung
But if we ask for --lines it gets b0rked:
[root@jouet ~]# perf annotate --stdio --no-source native_write_msr --print-line
Sorted summary for file /lib/modules/4.11.0-rc2+/build/vmlinux
----------------------------------------------
100.00 -nan 100.00 msr.h:104
Percent | Source code & Disassembly of vmlinux for cycles
(3 samples)
-------------------------------------------------------------------------------------------
: ffffffff81060bf0 <native_write_msr>:
: __wrmsr():
0.00 -nan 0.00 : ffffffff81060bf0: mov %edi,%ecx
0.00 -nan 0.00 : ffffffff81060bf2: mov %esi,%eax
0.00 -nan 0.00 : ffffffff81060bf4: wrmsr
: arch_static_branch():
msr.h:104 100.00 -nan 100.00 : ffffffff81060bf6: nopl
0x0(%rax,%rax,1)
: native_write_msr():
0.00 -nan 0.00 : ffffffff81060bfb: retq
0.00 -nan 0.00 : ffffffff81060bfc: push %rbp
0.00 -nan 0.00 : ffffffff81060bfd: mov %esi,%eax
0.00 -nan 0.00 : ffffffff81060bff: mov %rdx,%rsi
0.00 -nan 0.00 : ffffffff81060c02: shl $0x20,%rsi
0.00 -nan 0.00 : ffffffff81060c06: mov %eax,%edx
0.00 -nan 0.00 : ffffffff81060c08: mov %rsp,%rbp
0.00 -nan 0.00 : ffffffff81060c0b: or %rdx,%rsi
0.00 -nan 0.00 : ffffffff81060c0e: xor %edx,%edx
0.00 -nan 0.00 : ffffffff81060c10: callq ffffffff81457df0
<do_trace_write_msr>
0.00 -nan 0.00 : ffffffff81060c15: pop %rbp
0.00 -nan 0.00 : ffffffff81060c16: retq
[root@jouet ~]#
I don't have that much time to continue pursuing this, try to continue
investigating, I'll try to help and to fix this later.
- Arnaldo
