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

[Namhyung Kim]

On Mon, Mar 4, 2024 at 8:36 AM Namhyung Kim <namhyung@xxxxxxxxxx> wrote:
>
> Hi Arnaldo,
>
> On Mon, Mar 4, 2024 at 5:58 AM Arnaldo Carvalho de Melo <acme@xxxxxxxxxx> wrote:
> >
> > 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:
>
> Thanks for the test!  I think it missed the cast to 64-bit somewhere.
> I'll check and send v2 soon.

Yep, the offset variable in __symbol__inc_addr_samples()
should be u64.

Thanks,
Namhyung