Em Mon, Apr 13, 2015 at 06:34:38PM +0530, sahil aggarwal escreveu:
> Hi
>
> I am enabling sampling on tracepoint: sched:sched_switch, during which
> i get no data points for a particular process but when i run:
"sampling" what target? System wide? How are you setting up
perf_event_attr?
> perf stat -e "context_switch" <some exec>
s/context_switch/sched:sched_switch/g, right?
> then it shows that exec was context switched.
>
> How it could be possible.?
Why would it not?
[root@zoo ~]# perf stat -e sched:sched_switch usleep 1
Performance counter stats for 'usleep 1':
1 sched:sched_switch
0.001180692 seconds time elapsed
[root@zoo ~]#
[root@zoo ~]# perf trace --ev sched:sched_switch usleep 1 | tail
0.407 ( 0.004 ms): usleep/9676 mprotect(start: 0x601000, len: 4096, prot:
READ ) = 0
0.417 ( 0.005 ms): usleep/9676 mprotect(start: 0x7f1649452000, len: 4096,
prot: READ) = 0
0.429 ( 0.010 ms): usleep/9676 munmap(addr: 0x7f1649436000, len: 108577
) = 0
0.495 ( 0.002 ms): usleep/9676 brk(
) = 0xe5b000
0.500 ( 0.004 ms): usleep/9676 brk(brk: 0xe7c000
) = 0xe7c000
0.503 ( 0.001 ms): usleep/9676 brk(
) = 0xe7c000
0.525 ( 0.005 ms): usleep/9676 nanosleep(rqtp: 0x7fffc0c7f7e0
) ...
0.525 ( ): sched:sched_switch:usleep:9676 [120] S ==> swapper/2:0
[120])
0.582 ( 0.062 ms): usleep/9676 ... [continued]: nanosleep()) = 0
0.588 ( 0.000 ms): usleep/9676 exit_group(
[root@zoo ~]#
When we expected it to :-)
Now, this is how perf_event_attr is being set, in both cases (the code setting
up the perf_event_attr in 'perf trace' and 'perf stat' is the same):
[root@zoo ~]# perf stat -vv -e sched:sched_switch usleep 1
<SNIP>
perf_event_attr:
type 2
size 112
config 107
{ sample_period, sample_freq } 1
sample_type TIME|CPU|PERIOD|RAW
read_format TOTAL_TIME_ENABLED|TOTAL_TIME_RUNNING
disabled 1
inherit 1
enable_on_exec 1
exclude_guest 1
------------------------------------------------------------
sys_perf_event_open: pid 9685 cpu -1 group_fd -1 flags 0x8
sched:sched_switch: 1 688844 688844
Performance counter stats for 'usleep 1':
1 sched:sched_switch
0.001368517 seconds time elapsed
[root@zoo ~]#
[root@zoo ~]# perf trace -vv --ev sched:sched_switch usleep 1
<SNIP>
perf_event_attr:
type 2
size 112
config 107
{ sample_period, sample_freq } 1
sample_type IP|TID|TIME|ID|CPU|PERIOD|RAW
read_format ID
disabled 1
inherit 1
mmap 1
comm 1
enable_on_exec 1
task 1
sample_id_all 1
exclude_guest 1
mmap2 1
comm_exec 1
{ wakeup_events, wakeup_watermark } 1
<SNIP setting up the other events, for the syscall events>
0.491 ( 0.002 ms): usleep/9693 brk(
) = 0xd41000
0.502 ( 0.004 ms): usleep/9693 brk(brk: 0xd62000
) = 0xd62000
0.505 ( 0.002 ms): usleep/9693 brk(
) = 0xd62000
0.527 ( 0.005 ms): usleep/9693 nanosleep(rqtp: 0x7ffc7df44ee0
) ...
0.527 ( ): sched:sched_switch:usleep:9693 [120] S ==> swapper/1:0
[120])
0.583 ( 0.061 ms): usleep/9693 ... [continued]: nanosleep()) = 0
0.589 ( 0.000 ms): usleep/9693 exit_group(
[root@zoo ~]#
In the 'perf trace' case we need more stuff into sample_type, like ID, because
we need to map back to multiple events: sched:sched_switch,
raw_syscalls:sys_e{nter,xit}, etc.
- Arnaldo
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