[llvm-dev] [External] Re: Performance benefits shown in [RFC: CSSPGO with Pseudo-Instrumentation] can't be reproduced.

Tue Nov 2 02:16:37 PDT 2021

Can you send the results for each benchmark in SpecCPU2006 in detail
instead of Geometric? I can compare your results with SpecCPU2017 because
there are some common benchmarks in SpecCPU2006 and SpecCPU2017.

And in patch *https://reviews.llvm.org/D110081
<https://reviews.llvm.org/D110081>* <https://reviews.llvm.org/D110081>
I also have questions:

   1. Have you seen the compilation error when you use CSSPGO in
   SpecCPU2006? I seen the error in SpecCPU2017-502.gcc_r. This benchmark
   also exists in SpecCPU2006.
   2. About the fix, we may have better choice.* About the question: **Can
   we potentially lose contexts when an invalid line offset is one of the
   frames? Like A:-1 @ B:2 @ C:3, without this change, we could still have
   samples for B:2 @ C:3. But I think that's rare.*

   - You say that: you haven't seen those cases, it seems it only happened
   for leaf frame. Even it can be leaf call, there is no samples hit the
   callee. you can add a warning on the non-leaf frame invalid line of
   stack address.

   - As for me, I have seen the cases that happened for non-leaf frame. And
   if you filter out such callstack, the number of samples will decrease
   sharply. I haven't use the llvm-master successfully. After that I expect to
   show you.

If possible, I look forward to a voice conference with you if you are
 convenient at any time.

On Tue, Nov 2, 2021, 14:42 <xuqingqing.0729 at bytedance.com> wrote:

As you suggested, I remove -fdebug-info-for-profiling in first compiling
process and add -flto in second compiling process for CSSPGO, -flto can
bring great improvement.

To be fair, I also add -flto in second compiling process for AutoFDO. The
result shows that AutoFDO bring more performance benefits over CSSPGO
(about 20% on SpecCPU2017's 523.xalancbmk_r).

The version of llvm I used is llvm-12. And your RFC is also based on
llvm-12 according the time of RFC. Have I missed anything in the usage of
CSSPGO? Is there any option for CSSPGO which I need to open manually? Could
you please test the branch release/12.x and confirm the results to help me
to get performance benefits over AutoFDO?

Thanks,
Qingqing

On Sat, Oct 30, 2021, 04:53 <wlei at fb.com> wrote:

BTW, regarding the issue in
https://groups.google.com/g/llvm-dev/c/QJFIzk6bP1Y/m/8YlhrhXDAQAJ. (Sorry I
overlooked the message)

We have a fix in https://reviews.llvm.org/D110081 which can filter out the
negative LineOffset, you can have a try on latest llvm-profgen.

Thanks.

Lei

*From: *Hongtao Yu <hoy at fb.com>
*Date: *Friday, October 29, 2021 at 12:57 PM
*To: *Wenlei He <wenlei at fb.com>, 徐青青 <xuqingqing.0729 at bytedance.com>, via
llvm-dev <llvm-dev at lists.llvm.org>
*Cc: *Lei Wang <wlei at fb.com>
*Subject: *Re: [llvm-dev] Performance benefits shown in [RFC: CSSPGO with
Pseudo-Instrumentation] can't be reproduced.

Please also be noted that in order to maximize the benefit from CSSPGO and
its improved inlining, LTO mode is recommended. I suggest to try out -flto.

Thanks,

Hongtao

*From: *Wenlei He <wenlei at fb.com>
*Date: *Friday, October 29, 2021 at 12:49 PM
*To: *徐青青 <xuqingqing.0729 at bytedance.com>, via llvm-dev <
llvm-dev at lists.llvm.org>
*Cc: *Hongtao Yu <hoy at fb.com>, Lei Wang <wlei at fb.com>
*Subject: *Re: [llvm-dev] Performance benefits shown in [RFC: CSSPGO with
Pseudo-Instrumentation] can't be reproduced.

For Spec2017, we’ve seen 1%+ CPU improvements on Broadwell hosts in the
past. We use spec only for bringing up new technologies and we no longer
tracks spec results now as we move towards production workload. Also note
that the measurement was done on our internal fork, with some internal
patches. We’re still working on upstreaming some of them.

For the setup, -fdebug-info-for-profiling needs to be removed.

Thanks,

Wenlei

*From: *llvm-dev <llvm-dev-bounces at lists.llvm.org> on behalf of 徐青青 via
llvm-dev <llvm-dev at lists.llvm.org>
*Date: *Thursday, October 28, 2021 at 1:26 AM
*To: *via llvm-dev <llvm-dev at lists.llvm.org>
*Subject: *[llvm-dev] Performance benefits shown in [RFC: CSSPGO with
Pseudo-Instrumentation] can't be reproduced.

Hi All,

I am using *CSSPGO with Pseudo-Instrumentation*. But I found that the
performance benefits shown in [RFC: CSSPGO with Pseudo-Instrumentation]
<https://groups.google.com/g/llvm-dev/c/1p1rdYbL93s/m/iJjcmUS7AwAJ> *can't
be reproduced on Spec CPU 2017* based on *llvm-12*. In RFC, results show
that CSSPGO with Pseudo-Instrumentation achieves better performance over
AutoFDO.

Here, I have two question:

1.       Why choose Spec CPU 2006 instead of Spec CPU 2017? Do you have
results on Spec CPU 2017?

2.       Please point out if there is any error with my usage of CSSPGO,
the steps are as follows:

Suppose that my program is test.cpp.

Step 1: clang  -O3  -g3  -fno-omit-frame-pointer
 -fdebug-info-for-profiling  -fpseudo-probe-for-profiling  test.cpp  -o
 test

Step 2: perf  record  -g  --call-graph  fp  -e
 br_inst_retired.near_taken:uppp  -c  16009  -b  -o  test.perf.data  ./test

Step 3: perf  script  -F  ip,brstack  -i  test.perf.data  --show-mmap-event
 &>  test.perf.script

Step 4: llvm_install/bin/llvm-profgen  --perfscript=test.perf.script
 --binary=./test  --output=test.spgo.profraw  --format=text

Step 5: llvm_install/bin/llvm-profdata  merge  --text  --sample
 -output=test.spgo.prof  test.profraw ...

Step 6: clang  -O3  -g3  -fpseudo-probe-for-profiling
 --fprofile-sample-use=test.spgo.prof  test.cpp  -o  cs_test

Step 7: ./cs_test

Thanks,

Qingqing Xu

<*llvm-dev at lists.llvm.org>llvm-dev at lists.llvm.org
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