[PATCH] D36351: [lld][ELF] Add profile guided section layout

Rui Ueyama via llvm-commits llvm-commits at lists.llvm.org
Tue Oct 24 21:30:10 PDT 2017 

Unfortunately, even with --full-shutdown, the result was the same.

On Tue, Oct 24, 2017 at 9:25 PM, Rui Ueyama <ruiu at google.com> wrote:

> On Tue, Oct 24, 2017 at 9:23 PM, Michael Spencer <bigcheesegs at gmail.com>
> wrote:
>
>> On Tue, Oct 24, 2017 at 8:58 PM, Rui Ueyama <ruiu at google.com> wrote:
>>
>>> Sorry, as you pointed out, I made a mistake when I applied the patches.
>>> Now I succeeded to build it. But the output file of llvm-profdata seems too
>>> small. Is this correct?
>>>
>>> This is what I did.
>>>
>>> $ CC=`which clang` CXX=`which clang++` /ssd/cmake/bin/cmake -GNinja
>>> -DCMAKE_BUILD_TYPE=RelWithDebInfo -DLLVM_ENABLE_PROJECTS='clang;lld'
>>> -DCMAKE_C{,XX}_FLAGS=-fprofile-instr-generate ../llvm-project/llvm/
>>>
>>> $ ninja clang lld
>>>
>>> $ bin/ld.lld <options-to-link-clang>
>>>
>>> $ bin/llvm-profdata merge default.profraw -o default.profdata
>>>
>>> $ ls -l default.*
>>> -rw-r----- 1 ruiu eng     560 Oct 24 20:55 default.profdata
>>> -rw-r----- 1 ruiu eng 2151240 Oct 24 20:55 default.profraw
>>>
>>> $ bin/llvm-profdata show default.profraw
>>> error: default.profraw: Empty raw profile file
>>>
>>
>> It could be that lld is using quick exit and not properly flushing the
>> profile data to disk. I'll test out this configuration.
>>
>
> Ah, it's likely. I'll try again with `--full-shutdown` option.
>
>
>> - Michael Spencer
>>
>>
>>>
>>> On Mon, Oct 23, 2017 at 7:52 PM, Michael Spencer <bigcheesegs at gmail.com>
>>> wrote:
>>>
>>>> On Mon, Oct 23, 2017 at 6:53 PM, Rui Ueyama <ruiu at google.com> wrote:
>>>>
>>>>> It didn't pass cmake because lld/ELF/CMakeLists.txt lacked
>>>>> "CallGraphSort.cpp", so I added that to the CMakeLists.txt.
>>>>>
>>>>> It still didn't compile because `Config::CallGraphProfile` doesn't
>>>>> exist, so I added that boolean variable.
>>>>>
>>>>> /ssd/llvm-project/lld/ELF/CallGraphSort.cpp:274:29: error: no member
>>>>> named 'CallGraphProfile' in 'lld::elf::Configuration'
>>>>>   CallGraphSort CGS(Config->CallGraphProfile);
>>>>>                       ~~~~~~  ^
>>>>>
>>>>> Now, I'm seeing the following errors. How can I fix them?
>>>>>
>>>>> /ssd/llvm-project/lld/ELF/CallGraphSort.cpp:274:17: error: no
>>>>> matching constructor for initialization of '(anonymous
>>>>> namespace)::CallGraphSort'
>>>>>   CallGraphSort CGS(Config->CallGraphProfile);
>>>>>                 ^   ~~~~~~~~~~~~~~~~~~~~~~~~
>>>>> /ssd/llvm-project/lld/ELF/CallGraphSort.cpp:43:7: note: candidate
>>>>> constructor (the implicit copy constructor) not viable: no known conversion
>>>>> from 'bool' to 'const (anonymous namespace)::CallGraphSort' for 1st argument
>>>>> class CallGraphSort {
>>>>>       ^
>>>>> /ssd/llvm-project/lld/ELF/CallGraphSort.cpp:43:7: note: candidate
>>>>> constructor (the implicit move constructor) not viable: no known conversion
>>>>> from 'bool' to '(anonymous namespace)::CallGraphSort' for 1st argument
>>>>> class CallGraphSort {
>>>>>       ^
>>>>> /ssd/llvm-project/lld/ELF/CallGraphSort.cpp:115:16: note: candidate
>>>>> constructor not viable: no known conversion from 'bool' to
>>>>> 'DenseMap<std::pair<const SymbolBody *, const SymbolBody *>, uint64_t> &'
>>>>> (aka 'DenseMap<pair<const lld::elf::SymbolBody *, const
>>>>> lld::elf::SymbolBody *>, unsigned long> &') for 1st argument
>>>>> CallGraphSort::CallGraphSort(
>>>>>                ^
>>>>>
>>>>>
>>>> Are you sure you applied the patch correctly? I just checked the diff
>>>> and it has all that.
>>>>
>>>> diff --git a/ELF/CMakeLists.txt b/ELF/CMakeLists.txt
>>>> index 205702975..3b3c388d2 100644
>>>> --- a/ELF/CMakeLists.txt
>>>> +++ b/ELF/CMakeLists.txt
>>>> @@ -18,6 +18,7 @@ add_lld_library(lldELF
>>>>    Arch/SPARCV9.cpp
>>>>    Arch/X86.cpp
>>>>    Arch/X86_64.cpp
>>>> +  CallGraphSort.cpp
>>>>    Driver.cpp
>>>>    DriverUtils.cpp
>>>>    EhFrame.cpp
>>>>
>>>> It also has the change that adds CallGraphProfile to Config.h.
>>>>
>>>> - Michael Spencer
>>>>
>>>>
>>>>> On Mon, Oct 23, 2017 at 5:02 PM, Michael Spencer <
>>>>> bigcheesegs at gmail.com> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> - Michael Spencer
>>>>>>
>>>>>> On Tue, Oct 3, 2017 at 6:43 PM, Rui Ueyama via Phabricator <
>>>>>> reviews at reviews.llvm.org> wrote:
>>>>>>
>>>>>>> ruiu added a comment.
>>>>>>>
>>>>>>> Could you send me a patch to produce a call graph file so that I can
>>>>>>> try this patch on my machine?
>>>>>>>
>>>>>>
>>>>>> Sorry for the delay. I've attached the llvm and lld patches that
>>>>>> implement a full testable version of the feature.
>>>>>>
>>>>>> To use:
>>>>>>
>>>>>> -1) Have an elf system with working clang instrumentation based
>>>>>> profiling
>>>>>> 0) Compile clang and lld with the supplied patch
>>>>>> 1) Compile the code with `-fprofile-instr-generate` and link with any
>>>>>> linker
>>>>>> 2) Run the program on a representative sample
>>>>>> 3) `$ llvm-profdata merge default.profraw -o default.profdata`
>>>>>> 4) Compile the code again with `-fprofile-instr-use=default.profdata
>>>>>> -ffunction-sections -fuse-ld=lld`
>>>>>>
>>>>>> The output of #4 is the program with sections ordered by profile
>>>>>> data. You can add -Wl,-no-call-graph-profile-sort to disable sorting
>>>>>> to measure the difference.
>>>>>>
>>>>>> `llvm-readobj -elf-cg-profile` will dump the cg profile section.
>>>>>>
>>>>>> This also works with LTO.
>>>>>>
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:99-101
>>>>>>> +  if (To != Other.To)
>>>>>>> +    return To < Other.To;
>>>>>>> +  return false;
>>>>>>> ----------------
>>>>>>> You can just return `To < Other.To`.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:127
>>>>>>> +  // Create the graph.
>>>>>>> +  for (const auto &C : Profile) {
>>>>>>> +    if (C.second == 0)
>>>>>>> ----------------
>>>>>>> This loop is a bit too dense. It cannot be understood without
>>>>>>> reading each line carefully as I don't understand the whole picture. Please
>>>>>>> insert a blank line between code blocks. Adding more comment would help.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:128
>>>>>>> +  for (const auto &C : Profile) {
>>>>>>> +    if (C.second == 0)
>>>>>>> +      continue;
>>>>>>> ----------------
>>>>>>> Please define local variables for `C.first.first`, `C.first.second`
>>>>>>> and `C.second` so that they are accessed through meaningful names.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:130-135
>>>>>>> +    auto FromDR = dyn_cast_or_null<DefinedRegula
>>>>>>> r>(Symtab->find(C.first.first));
>>>>>>> +    auto ToDR = dyn_cast_or_null<DefinedRegula
>>>>>>> r>(Symtab->find(C.first.second));
>>>>>>> +    if (!FromDR || !ToDR)
>>>>>>> +      continue;
>>>>>>> +    auto FromSB = dyn_cast_or_null<const
>>>>>>> InputSectionBase>(FromDR->Section);
>>>>>>> +    auto ToSB = dyn_cast_or_null<const
>>>>>>> InputSectionBase>(ToDR->Section);
>>>>>>> ----------------
>>>>>>> auto -> auto *
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:147
>>>>>>> +      Nodes[To].IncidentEdges.push_back(EI);
>>>>>>> +    } else
>>>>>>> +      Edges[EI].Weight = SaturatingAdd(Edges[EI].Weight, C.second);
>>>>>>> ----------------
>>>>>>> nit: add {}
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:153
>>>>>>> +
>>>>>>> +void CallGraphSort::contractEdge(EdgeIndex CEI) {
>>>>>>> +  // Make a copy of the edge as the original will be marked killed
>>>>>>> while being
>>>>>>> ----------------
>>>>>>> Please add a function comment as to what this function is intended
>>>>>>> to do. I do not understand this function because I don't get a whole
>>>>>>> picture.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:158-163
>>>>>>> +  // Remove the self edge from From.
>>>>>>> +  FE.erase(std::remove(FE.begin(), FE.end(), CEI));
>>>>>>> +  std::vector<EdgeIndex> &TE = Nodes[CE.To].IncidentEdges;
>>>>>>> +  // Update all edges incident with To to reference From instead.
>>>>>>> Then if they
>>>>>>> +  // aren't self edges add them to From.
>>>>>>> +  for (EdgeIndex EI : TE) {
>>>>>>> ----------------
>>>>>>> Add blank lines before comments.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:165-166
>>>>>>> +    Edge &E = Edges[EI];
>>>>>>> +    // E.From = E.From == CE.To ? CE.From : E.From;
>>>>>>> +    // E.To = E.To == CE.To ? CE.From : E.To;
>>>>>>> +    if (E.From == CE.To)
>>>>>>> ----------------
>>>>>>> Please remove debug code.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:178-180
>>>>>>> +  // Free memory.
>>>>>>> +  std::vector<EdgeIndex>().swap(TE);
>>>>>>> +
>>>>>>> ----------------
>>>>>>> This looks odd. Why do you need to do this? I think you can just
>>>>>>> leave it alone.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:207-208
>>>>>>> +
>>>>>>> +// Group InputSections into clusters using the Call-Chain
>>>>>>> Clustering heuristic
>>>>>>> +// then sort the clusters by density.
>>>>>>> +void CallGraphSort::generateClusters() {
>>>>>>> ----------------
>>>>>>> This might be understood for those who read the paper, but I don't
>>>>>>> think that is enough. Please write more comment as to what are clusters,
>>>>>>> what is density, and what is the heuristic.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/CallGraphSort.cpp:272-273
>>>>>>> +DenseMap<const InputSectionBase *, int>
>>>>>>> elf::computeCallGraphProfileOrder() {
>>>>>>> +  CallGraphSort CGS(Config->CallGraphProfile);
>>>>>>> +  return CGS.run();
>>>>>>> +}
>>>>>>> ----------------
>>>>>>> You can do this in one line without defining a local variable.
>>>>>>>
>>>>>>>
>>>>>>> ================
>>>>>>> Comment at: ELF/Writer.cpp:926-928
>>>>>>> +    for (BaseCommand *Base : Script->Opt.Commands)
>>>>>>> +      if (auto *OS = dyn_cast<OutputSection>(Base))
>>>>>>> +        if (OS->Name == ".text") {
>>>>>>> ----------------
>>>>>>> I'd factor this code out as `OutputSection
>>>>>>> *findOutputSection(StringRef Name)`.
>>>>>>>
>>>>>>>
>>>>>>> https://reviews.llvm.org/D36351
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>>
>>>>>>
>>>>>
>>>>
>>>
>>
>
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