Bug 3342

Summary: perf script: improve 'live mode'
Product: [Build System, Metadata & Runtime] OE-Core Reporter: Tom Zanussi <tom.zanussi>
Component: kernelAssignee: Tom Zanussi <tom.zanussi>
Status: RESOLVED INVALID QA Contact:
Severity: enhancement    
Priority: Low CC: bruce.ashfield, dvhart, joshuagloe, tom.zanussi
Version: 1.4   
Target Milestone: Future   
Hardware: x86   
OS: Multiple   
Whiteboard:
OS type for building Yocto: --- Type of Regression: ---
Verified: Documentation change: Don't know

Description Tom Zanussi 2012-10-26 22:45:43 UTC 
The 'live mode' in perf script essentially sends the stdout of the record process to the stdin of the report process through a pipe.  This is OK for low-volume events e.g. for 'perf script rwtop', but breaks down at high volume:

root@crownbay:~# perf script sctop

syscall events:

event                                          count
----------------------------------------  ----------
3                                              88768
240                                             1208
4                                                127
54                                                51
265                                               18
168                                               18
102                                               18
142                                               14
192                                               12
104                                               12
91                                                12
78                                                12
13                                                10
146                                                6
43                                                 4
195                                                2
197                                                1
^CWarning:
Processed 589913 events and lost 179 chunks!

Check IO/CPU overload!

There also seems to be some kind of drawing problem with the display for this script as you can see it visibly drawing line by line.
Comment 1 Tom Zanussi 2013-01-18 20:49:35 UTC 
As a start to this, I've sent out a patchset to lkml that fixes various related problems:

http://www.mail-archive.com/linux-kernel@vger.kernel.org/msg370505.html

In a lot of cases the high loads are a result of tracing perf-related activity, so I also experimented with the event filters to screen out perf-originated events.

e.g. to screen out perf write events:

[root@empanada ~]# export x=`expr \`ls /proc/self/task\` + 1`;perf record -a -e syscalls:sys_enter_read -e syscalls:sys_exit_read -e syscalls:sys_enter_write --filter "common_pid != $x" -e syscalls:sys_exit_write  --filter "common_pid != $x

This works but is pretty unwieldy - need to try to come up with an easier interface that still uses the kernel event filtering engine.
Comment 2 Joshua Lock 2017-06-13 11:12:57 UTC 
This bug is tracking an enhancement to perf which does not fall under the YP umbrella.