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SubjectRe: [PATCH] perf report: Fix no libunwind compiled warning break s390 issue
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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@linux.ibm.com>
>> Tested-by: Thomas Richter <tmricht@linux.ibm.com>
>> Signed-off-by: Jin Yao <yao.jin@linux.intel.com>
>
> 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@redhat.com>
>
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
>>
>

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