[liburing,v1,0/2] __hot and __cold

Message

Ammar Faizi July 3, 2022, 11:59 a.m. UTC

From: Ammar Faizi <[e-mail]>

Hi Jens,

This series adds __hot and __cold macros. Currently, the __hot macro
is not used. The __cold annotation hints the compiler to optimize for
code size. This is good for the slow-path in the setup.c file.

Here is the result compiling with Ubuntu clang
15.0.0-++20220601012204+ec2711b35411-1~exp1~20220601012300.510

Without this patchset:

  $ wc -c src/liburing.so.2.3
  71288 src/liburing.so.2.3

With this patchset:

  $ wc -c src/liburing.so.2.3
  69448 src/liburing.so.2.3

Take one slow-path function example, using __cold avoids aggresive
inlining.

Without this patchset:

  00000000000024f0 <io_uring_queue_init>:
    24f0: pushq  %r14
    24f2: pushq  %rbx
    24f3: subq   $0x78,%rsp
    24f7: movq   %rsi,%r14
    24fa: xorps  %xmm0,%xmm0
    24fd: movaps %xmm0,(%rsp)
    2501: movaps %xmm0,0x60(%rsp)
    2506: movaps %xmm0,0x50(%rsp)
    250b: movaps %xmm0,0x40(%rsp)
    2510: movaps %xmm0,0x30(%rsp)
    2515: movaps %xmm0,0x20(%rsp)
    251a: movaps %xmm0,0x10(%rsp)
    251f: movq   $0x0,0x70(%rsp)
    2528: movl   %edx,0x8(%rsp)
    252c: movq   %rsp,%rsi
    252f: movl   $0x1a9,%eax
    2534: syscall
    2536: movq   %rax,%rbx
    2539: testl  %ebx,%ebx
    253b: js     256a <io_uring_queue_init+0x7a>
    253d: movq   %rsp,%rsi
    2540: movl   %ebx,%edi
    2542: movq   %r14,%rdx
    2545: callq  2080 <io_uring_queue_mmap@plt>
    254a: testl  %eax,%eax
    254c: je     255d <io_uring_queue_init+0x6d>
    254e: movl   %eax,%edx
    2550: movl   $0x3,%eax
    2555: movl   %ebx,%edi
    2557: syscall
    2559: movl   %edx,%ebx
    255b: jmp    256a <io_uring_queue_init+0x7a>
    255d: movl   0x14(%rsp),%eax
    2561: movl   %eax,0xc8(%r14)
    2568: xorl   %ebx,%ebx
    256a: movl   %ebx,%eax
    256c: addq   $0x78,%rsp
    2570: popq   %rbx
    2571: popq   %r14
    2573: retq

With this patchset:

  000000000000240c <io_uring_queue_init>:
    240c: subq   $0x78,%rsp
    2410: xorps  %xmm0,%xmm0
    2413: movq   %rsp,%rax
    2416: movaps %xmm0,(%rax)
    2419: movaps %xmm0,0x60(%rax)
    241d: movaps %xmm0,0x50(%rax)
    2421: movaps %xmm0,0x40(%rax)
    2425: movaps %xmm0,0x30(%rax)
    2429: movaps %xmm0,0x20(%rax)
    242d: movaps %xmm0,0x10(%rax)
    2431: movq   $0x0,0x70(%rax)
    2439: movl   %edx,0x8(%rax)
    243c: movq   %rax,%rdx
    243f: callq  2090 <io_uring_queue_init_params@plt>
    2444: addq   $0x78,%rsp
    2448: retq

Signed-off-by: Ammar Faizi <[e-mail]>
---

Ammar Faizi (2):
  lib: Add __hot and __cold macros
  setup: Mark the exported functions as __cold

 src/lib.h   |  2 ++
 src/setup.c | 25 ++++++++++++++-----------
 2 files changed, 16 insertions(+), 11 deletions(-)


base-commit: 98c14a04e2c0dcdfbb71372a1a209ed889fb3e4d

Comments

Jens Axboe July 3, 2022, 1 p.m. UTC | #1

On Sun, 3 Jul 2022 18:59:10 +0700, Ammar Faizi wrote:
> From: Ammar Faizi <[e-mail]>
> 
> Hi Jens,
> 
> This series adds __hot and __cold macros. Currently, the __hot macro
> is not used. The __cold annotation hints the compiler to optimize for
> code size. This is good for the slow-path in the setup.c file.
> 
> [...]

Applied, thanks!

[1/2] lib: Add __hot and __cold macros
      commit: ee459df3c83ab86b84e1acaaa23c340efb5bab35
[2/2] setup: Mark the exported functions as __cold
      commit: 907c171fa4aac773fee9421bc38fcf9581e54f61

Best regards,