Re: Some newbie questions

[Avi Kivity <avi at scylladb dot com>]

On 08/09/2016 06:17 PM, David Smith wrote:
> On 08/09/2016 01:51 AM, Avi Kivity wrote:
> > On 08/08/2016 05:58 PM, David Smith wrote:
> > > > 2. Inlined functions
> > > >
> > > >   From the manual pages, it seems that inlined functions can be probed
> > > > (minus the .return probe), but I just get an error:
> > > >
> > > > semantic error: while resolving probe point: identifier 'process' at
> > > > script/home/avi/seastar/debug/task-latency.stap:3:7
> > > >           source: probe
> > > > process("scylla").function("reactor::run_tasks()") {
> > > >                         ^
> > > >
> > > > semantic error: no match (similar functions:
> > > > _ZN7reactor14run_exit_tasksEv, statfs, dup, mkdir, ntohs)
> > > We're at the mercy of the compiler and the quality of the debuginfo it
> > > produces here when looking for inlined functions.
> > >
> > > If you want to investigate further here, you'll need to do the following:
> > >
> > > # eu-readelf -N --debug-dump=info scylla > scylla.log
> > >
> > > In scylla.log, look and see if you can find a subprogram with the name
> > > of the function you are interested in.
> >   [1417f4]      subprogram
> >                 external             (flag_present) Yes
> >                 name                 (strp) "run_tasks"
> >                 decl_file            (data1) 5
> >                 decl_line            (data2) 812
> >                 linkage_name         (strp)
> > "_ZN7reactor9run_tasksER15circular_bufferISt10unique_ptrI4taskSt14default_deleteIS2_EESaIS5_EE"
> >
> >                 declaration          (flag_present) Yes
> >                 object_pointer       (ref4) [141808]
> >                 sibling              (ref4) [141813]
> >   [141808]        formal_parameter
> >                   type                 (ref4) [1423bd]
> >                   artificial           (flag_present) Yes
> >   [14180d]        formal_parameter
> >                   type                 (ref4) [14a8a8]
> According to the above, that function isn't inlined. You might just try
> the following to see what functions stap can see:
>
> # stap -l 'process("scylla").function("*")' | grep run_tasks

process("/usr/bin/scylla").function("run_tasks@core/reactor.cc:1362")

Strangely not qualified by "reactor::".

> > I also switched to timer.profile.  What's its resolution on normal
> > machines?
> timer.profile probe resolution is CONFIG_HZ. Check your kernel config
> and see "man stapprobes" for more details.

Thanks.