Feature #10050: [PATCH 0/2] reduce rb_io_t to 192 bytes (from 216) on 64-bit

• Status: Closed
• Assignee: normalperson (Eric Wong)
• Target version: 2.2.0

[normalperson (Eric Wong)]

This will allow x86-64 machines to only use 3 cache lines instead of 4
(where cache size == 64).

Hopefully there are other 64-bit architectures which benefit, too.

This is also public ABI breakage, so I hope to commit it around when a patch for
Feature #10034 (re_pattern_buffer reduction) gets committed to reduce testers'
need to rebuild C exts.

[normalperson (Eric Wong)]

• File 0001-rb_io_t.patch 0001-rb_io_t.patch added

[normalperson (Eric Wong)]

• File 0002-rb_io_buffer_t.patch 0002-rb_io_buffer_t.patch added

[normalperson (Eric Wong)]

I forgot to note this the last publically-visible struct which may be
packed. Internals for the others are defined privately:

$ pahole -P ruby
rb_thread_struct	1016	1000	16
rb_execarg	160	152	8
io_internal_writev_struct	24	16	8
io_advise_struct	32	24	8
waitpid_arg	24	16	8
load_file_arg	48	40	8
rb_econv_t	200	184	16
rb_transcoder	160	152	8
rb_context_struct	1312	1304	8
rb_fiber_struct	2304	2296	8
parser_params	320	304	16

• Status changed from Open to Closed
• % Done changed from 0 to 100

Applied in changeset r46883.

---

rb_io_t: shrink from 216 to 200 bytes on 64-bit

• include/ruby/io.h (rb_io_t): shrink to 200 bytes from 216 on 64-bit
  This puts us within 8 bytes of being three cache lines instead of
  four lines on x86-64. This breaks the ABI.
  [Feature #10050]

[ngoto (Naohisa Goto)]

• Related to Bug #10088: Bus Error on Sparc Solaris since r46884 added