What helps with stacks?

What helps with stacks?

[Daniel Speyer]

Hello all,

I'm trying to get stack traces for a bunch of events using perf record and
having trouble with them getting cut off.  I'm using --callgraph dwarf,
which helps a little, and I recompiled libc with --fno-omit-frame-pointer,
which doesn't seem to have helped at all.  Very often, the bottom of the
stack is in libc, often __epoll_wait_nocancel.  Stacks for
sched:sched_switch events seem to be worse than cycles or sched:sched_wakeup
events, but it isn't 100%.  Is there anything else I could try?

Thanks,
--Daniel Speyer

Re: What helps with stacks?

[Andi Kleen]

Daniel Speyer <dspeyer@gmail.com> writes:

> Hello all,
>
> I'm trying to get stack traces for a bunch of events using perf record and
> having trouble with them getting cut off.  I'm using --callgraph dwarf,
> which helps a little, and I recompiled libc with --fno-omit-frame-pointer,
> which doesn't seem to have helped at all.  Very often, the bottom of the
> stack is in libc, often __epoll_wait_nocancel.  Stacks for
> sched:sched_switch events seem to be worse than cycles or sched:sched_wakeup
> events, but it isn't 100%.  Is there anything else I could try?


If you have a Haswell/Broadwell system and uptodate perf (4.0) you can also
use --call-graph lbr

This uses a new hardware mechanism that can handle many situations
where the old ones failed (but also has some situations where
it has to give up)

-andi


-- 
ak@linux.intel.com -- Speaking for myself only

Re: What helps with stacks?

[Daniel Speyer]

Andi Kleen <andi <at> firstfloor.org> writes:
> If you have a Haswell/Broadwell system and uptodate perf (4.0) you can also
> use --call-graph lbr
> 
> This uses a new hardware mechanism that can handle many situations
> where the old ones failed (but also has some situations where
> it has to give up)
> 
> -andi
> 

We've gotten access to a Haswell system.  How do we get perf with LBR
support?  It looks like it hasn't been merged into the main line kernel. 
Are there binaries anywhere?  Do we need to upgrade the entire kernel, or
just the perf utility?