Re: [PATCH] perf report: Fix no libunwind compiled warning break s390 issue

[Jin, Yao]

On 1/8/2020 6:27 PM, Jiri Olsa wrote:
> On Wed, Jan 08, 2020 at 03:17:45AM +0800, Jin Yao wrote:
> > Commit 800d3f561659 ("perf report: Add warning when libunwind not compiled in")
> > breaks the s390 platform. S390 uses libdw-dwarf-unwind for call chain
> > unwinding and had no support for libunwind.
> >
> > So the warning "Please install libunwind development packages during the perf build."
> > caused the confusion even if the call-graph is displayed correctly.
> >
> > This patch adds checking for HAVE_DWARF_SUPPORT, which is set when
> > libdw-dwarf-unwind is compiled in.
> >
> > Fixes: 800d3f561659 ("perf report: Add warning when libunwind not compiled in")
> >
> > Reviewed-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> > Tested-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
> > Signed-off-by: Jin Yao <yao.jin@xxxxxxxxxxxxxxx>
>
> perfect, I have the same change prepared for sending, but it's
> together with making libdw default dwarf unwinder, which I'm still
> not sure we want to do, so it all got posponed ;-)
>  > would you guys be ok with that? with having libdw picked up as 
default dwarf unwinder..
>

I've roughly compared the performance between libunwind-dev and 
libdw-dev. While in my test (on KBL desktop), for the same perf report 
command-line, it looks the perf built with libunwind-dev is much faster 
than the perf built with libdw-dev.

The command line is as following:

perf record --call-graph dwarf ./div
perf report -g graph --stdio

Maybe you give it a try. :)

> for the patch:
>
> Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Thanks for reviewing the patch.

Thanks
Jin Yao

> thanks,
> jirka
>
> > ---
> >   tools/perf/builtin-report.c | 6 +++---
> >   1 file changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/tools/perf/builtin-report.c b/tools/perf/builtin-report.c
> > index de988589d99b..66cd97cc8b92 100644
> > --- a/tools/perf/builtin-report.c
> > +++ b/tools/perf/builtin-report.c
> > @@ -412,10 +412,10 @@ static int report__setup_sample_type(struct report *rep)
> >   				PERF_SAMPLE_BRANCH_ANY))
> >   		rep->nonany_branch_mode = true;
> >   
> > -#ifndef HAVE_LIBUNWIND_SUPPORT
> > +#if !defined(HAVE_LIBUNWIND_SUPPORT) && !defined(HAVE_DWARF_SUPPORT)
> >   	if (dwarf_callchain_users) {
> > -		ui__warning("Please install libunwind development packages "
> > -			    "during the perf build.\n");
> > +		ui__warning("Please install libunwind or libdw "
> > +			    "development packages during the perf build.\n");
> >   	}
> >   #endif
> >   
> > --
> > 2.17.1