Re: [PATCHv3 00/12] perf tools: Display eBPF code in intel_pt trace

Leo Yan
2019-05-30T12:57:22Z

Hi Jiri,

On Thu, May 30, 2019 at 02:07:10PM +0200, Jiri Olsa wrote:
> On Thu, May 30, 2019 at 06:54:39PM +0800, Leo Yan wrote:
> > Hi Jiri,
> >
> > On Wed, May 08, 2019 at 03:19:58PM +0200, Jiri Olsa wrote:
> > > hi,
> > > this patchset adds dso support to read and display
> > > bpf code in intel_pt trace output. I had to change
> > > some of the kernel maps processing code, so hopefully
> > > I did not break too many things ;-)
> > >
> > > It's now possible to see bpf code flow via:
> > >
> > > # perf-with-kcore record pt -e intel_pt//ku -- sleep 1
> > > # perf-with-kcore script pt --insn-trace --xed
> >
> > This is very interesting work for me!
> >
> > I want to verify this feature with Arm CoreSight trace, I have one
> > question so that I have more direction for the tesing:
> >
> > What's the bpf program you are suing for the testing? e.g. some
> > testing program under the kernel's folder $kernel/samples/bpf?
> > Or you uses perf command to launch bpf program?
>
> for this I was using tools/testing/selftests/bpf/test_verifier
>
> I isolated some tests and ran the perf on top of them, like:
>
> # perf-with-kcore record pt -e intel_pt//ku -- ./test_verifier ...

Thanks a lot for sharing the info and quick responsing.

I tried to use the program $kernel/samples/bpf/sampleip to verify this
patch set, but seems eBPF dso is not contained properly; below is my
detailed steps:

# In the first tty
# cd $kernel/samples/bpf/
# ./sampleip -F 200 20 => sample ip with 200Hz for 20s

# In the second tty
# perf-with-kcore record arm_test -e cs_etm/@20070000.etr/uk -- sleep 1

If I output DSO info with report command it give below info, which
doesn't contain any info for eBPF DSO?

# perf-with-kcore report arm_test -F,dso

# Samples: 6M of event 'branches:ku'
# Event count (approx.): 6340896
#
# Shared Object
# ..................
#
[kernel.kallsyms]
ld-2.28.so
libc-2.28.so
libpthread-2.28.so
perf
sleep
[unknown]

> I had to add some small sleep before the test_verifier exit,
> so the perf bpf thread could catch up and download the program
> details before test_verifier exited.

This seems to me for a 'real' eBPF program, do we also need extra sleep
so that perf bpf can save dso properly?

BTW, I have another question: to display eBPF code, except this feature
can be used by hardware tracing (e.g. intel_pt), it also can be used
by other PMU events and timer events, right?

Thanks,
Leo Yan