[PATCH] D36351: [lld][ELF] Add profile guided section layout
Michael Spencer via llvm-commits
llvm-commits at lists.llvm.org
Tue Oct 24 21:23:15 PDT 2017
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.
- 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->Sectio
>>>>> n);
>>>>> ----------------
>>>>> 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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