Re: [PATCH 3/5] perf core: Prepare writing into ring buffer from end

[Wangnan (F)]

On 2016/3/25 20:36, Wangnan (F) wrote:
> On 2016/3/25 20:26, Wangnan (F) wrote:
> > On 2016/3/23 17:50, Peter Zijlstra wrote:
> > > On Mon, Mar 14, 2016 at 09:59:43AM +0000, Wang Nan wrote:
> > > > Convert perf_output_begin to __perf_output_begin and make the later
> > > > function able to write records from the end of the ring buffer.
> > > > Following commits will utilize the 'backward' flag.
> > > >
> > > > This patch doesn't introduce any extra performance overhead since we
> > > > use always_inline.
> > > So while I agree that with __always_inline and constant propagation we
> > > _should_ end up with the same code, we have:
> > >
> > > $ size defconfig-build/kernel/events/ring_buffer.o.{pre,post}
> > >     text    data     bss     dec     hex filename
> > >     3785       2       0    3787     ecb 
> > > defconfig-build/kernel/events/ring_buffer.o.pre
> > >     3673       2       0    3675     e5b 
> > > defconfig-build/kernel/events/ring_buffer.o.post
> > >
> > > The patch actually makes the file shrink.
> > >
> > > So I think we still want to have some actual performance numbers.
> >
> > In my environment the two objects are nearly idential:
> >
> >
> > $ objdump -d kernel/events/ring_buffer.o.new  > ./out.new.S
> > $ objdump -d kernel/events/ring_buffer.o.old  > ./out.old.S
> >
> > --- ./out.old.S    2016-03-25 12:18:52.060656423 +0000
> > +++ ./out.new.S    2016-03-25 12:18:45.376630269 +0000
> > @@ -1,5 +1,5 @@
> >
> > -kernel/events/ring_buffer.o.old:     file format elf64-x86-64
> > +kernel/events/ring_buffer.o.new:     file format elf64-x86-64
> >
> >
> >  Disassembly of section .text:
> > @@ -320,7 +320,7 @@
> >   402:    4d 8d 04 0f              lea    (%r15,%rcx,1),%r8
> >   406:    48 89 c8                 mov    %rcx,%rax
> >   409:    4c 0f b1 43 40           cmpxchg %r8,0x40(%rbx)
> > - 40e:    48 39 c8                 cmp    %rcx,%rax
> > + 40e:    48 39 c1                 cmp    %rax,%rcx
> >   411:    75 b4                    jne    3c7 <perf_output_begin+0xc7>
> >   413:    48 8b 73 58              mov    0x58(%rbx),%rsi
> >   417:    48 8b 43 68              mov    0x68(%rbx),%rax
> > @@ -357,7 +357,7 @@
> >   480:    85 c0                    test   %eax,%eax
> >   482:    0f 85 02 ff ff ff        jne    38a <perf_output_begin+0x8a>
> >   488:    48 c7 c2 00 00 00 00     mov    $0x0,%rdx
> > - 48f:    be 7c 00 00 00           mov    $0x7c,%esi
> > + 48f:    be 89 00 00 00           mov    $0x89,%esi
> >   494:    48 c7 c7 00 00 00 00     mov    $0x0,%rdi
> >   49b:    c6 05 00 00 00 00 01     movb   $0x1,0x0(%rip) # 4a2 
> > <perf_output_begin+0x1a2>
> >   4a2:    e8 00 00 00 00           callq  4a7 <perf_output_begin+0x1a7>
> > @@ -874,7 +874,7 @@
> >   c39:    eb e7                    jmp    c22 
> > <perf_aux_output_begin+0x172>
> >   c3b:    80 3d 00 00 00 00 00     cmpb   $0x0,0x0(%rip) # c42 
> > <perf_aux_output_begin+0x192>
> >   c42:    75 93                    jne    bd7 
> > <perf_aux_output_begin+0x127>
> > - c44:    be 2b 01 00 00           mov    $0x12b,%esi
> > + c44:    be 49 01 00 00           mov    $0x149,%esi
> >   c49:    48 c7 c7 00 00 00 00     mov    $0x0,%rdi
> >   c50:    e8 00 00 00 00           callq  c55 
> > <perf_aux_output_begin+0x1a5>
> >   c55:    c6 05 00 00 00 00 01     movb   $0x1,0x0(%rip) # c5c 
> > <perf_aux_output_begin+0x1ac>
> >
> >
> > I think you enabled some unusual config options?
>
> You must enabled CONFIG_OPTIMIZE_INLINING. Now I get similar result:
>
> $ size kernel/events/ring_buffer.o*
>    text       data        bss        dec        hex    filename
>    4545          4          8       4557       11cd 
> kernel/events/ring_buffer.o.new
>    4641          4          8       4653       122d 
> kernel/events/ring_buffer.o.old
>
> Thank you.

After enabling CONFIG_OPTIMIZE_INLINING:

Test its performance by calling 'close(-1)' for 3000000 times and
use 'perf record -o /dev/null -e raw_syscalls:* test-ring-buffer' to
capture system calls:

                  MEAN         STDVAR
BASE            800077.1     23448.13
RAWPERF.PRE    2465858.0    603473.70
RAWPERF.POST   2471925.0    609437.60

Considering the high stdvar, after applying this patch the performance
is not change.

I'll put this number in my commit message.

Thank you.