Re: [PATCH 0/4] perf annotate: Improve memory usage for symbol histogram

[Arnaldo Carvalho de Melo <acme@kernel.org>]

On Tue, Feb 27, 2024 at 04:52:26PM -0800, Namhyung Kim wrote:
> This is another series of memory optimization in perf annotate.
 
> When perf annotate (or perf report/top with TUI) processes samples, it
> needs to save the sample period (overhead) at instruction level.  For
> now, it allocates an array to do that for the whole symbol when it
> hits any new symbol.  This comes with a lot of waste since samples can
> be very few and instructions span to multiple bytes.
 
> For example, when a sample hits symbol 'foo' that has size of 100 and
> that's the only sample falls into the symbol.  Then it needs to
> allocate a symbol histogram (sym_hist) and the its size would be
 
>   16 (header) + 16 (sym_hist_entry) * 100 (symbol_size) = 1616
 
> But actually it just needs 32 (header + sym_hist_entry) bytes.  Things
> get worse if the symbol size is bigger (and it doesn't have many
> samples in different places).  Also note that it needs separate
> histogram for each event.
 
> Let's split the sym_hist_entry and have it in a hash table so that it
> can allocate only necessary entries.
 
> No functional change intended.

I tried this before/after this series:

  $ time perf annotate --stdio2 -i perf.data.annotate

For:

  perf record -e '{cycles,instructions,cache-misses}' make -k CORESIGHT=1 O=/tmp/build/$(basename $PWD)/ -C tools/perf install-bin

And found these odd cases:

  $ diff -u before after
  --- before	2024-02-28 15:38:25.086062812 -0300
  +++ after	2024-02-29 14:12:05.606652725 -0300
  @@ -2450826,7 +2450826,7 @@
                                ↓ je       1c62                  
                                → call     operator delete(void*)@plt
                                { return _M_dataplus._M_p; }
  -                       1c62:   mov      0x13c0(%rsp),%rdi     
  +  0.00   0.00 100.00   1c62:   mov      0x13c0(%rsp),%rdi     
                                if (_M_data() == _M_local_data())
                                  lea      0x13d0(%rsp),%rax     
                                  cmp      %rax,%rdi             
  @@ -2470648,7 +2470648,7 @@
                                  mov      %rbx,%rdi             
                                → call     operator delete(void*)@plt
                                using reference = T &;     
  -  0.00   0.00 100.00  11c65:   mov      0x8(%r12),%rax        
  +                      11c65:   mov      0x8(%r12),%rax        
                                size_t size() const { return Size; }
                                  mov      0x10(%r12),%ecx       
                                  mov      %rax,%rbp             
  $


This is a large function:

Samples: 574K of events 'anon group { cpu_core/cycles/u, cpu_core/instructions/u, cpu_core/cache-misses/u }', 4000 Hz, Event count (approx.): 614695751751, [percent: local period]$
clang::CompilerInvocation::ParseCodeGenArgs(clang::CodeGenOptions&, llvm::opt::ArgList&, clang::InputKind, clang::DiagnosticsEngine&, llvm::Triple const&, std::__cxx11::basic_string<char, std
Percent 

Probably when building the BPF skels in tools/perf/

- Arnaldo