Misc #15007: Let all Init_xxx and extension APIs frequently called from init code paths be considered cold

• Status: Assigned
• Assignee: naruse (Yui NARUSE)

[methodmissing (Lourens Naudé)]

References Github PR https://github.com/ruby/ruby/pull/1934

Why?

An incremental extraction from PR https://github.com/ruby/ruby/pull/1922, specifically addressing the feedback from Yui Naruse in https://github.com/ruby/ruby/pull/1922#issuecomment-413796710

The Linux kernel, PHP 7 and other projects use the hot and cold function attributes to help with better code layout.

I noticed Ruby is very much CPU frontend bound (not feeding instructions into the CPU pipelines as fast as it maybe could) and therefore even most micro benchmarks have a high CPI (cycles per instruction) rate. This PR is part of a larger chunk of work I'd like to do around improving CPU frontend throughput and can take a stab at formally writing up those ideas if there's any interest from the community. I don't know.

Implementation

This PR has an exclusive focus on having the Init_xxx functions for the core classes and those bundled in ext being flagged to be optimized for size as they're called only once at runtime.

The GCC specific cold function attribute works in the following way (from GCC docs):

The cold attribute is used to inform the compiler that a function is unlikely executed. The function is optimized for size rather than speed and on many targets it is placed into special subsection of the text section so all cold functions appears close together improving code locality of non-cold parts of program. The paths leading to call of cold functions within code are marked as unlikely by the branch prediction mechanism. It is thus useful to mark functions used to handle unlikely conditions, such as perror, as cold to improve optimization of hot functions that do call marked functions in rare occasions.
When profile feedback is available, via -fprofile-use, hot functions are automatically detected and this attribute is ignored.

By declaring a function as cold when defined we get the following benefits:

• No-op on platforms that does not support the attribute
• Size optimization of cold functions with a smaller footprint in the instruction cache
• Therefore CPU frontend throughput increases due to a lower ratio of instruction cache misses and a lower ITLB overhead - see original chunky PR VS then trunk
• This effect can further be amplified in future work with the hot attribute

Extension APIs flagged as cold

These are and should typically only be called on extension init, and thus safe to optimize for size as well.

• void rb_define_method_id(VALUE, ID, VALUE (*)(ANYARGS), int));
• void rb_undef(VALUE, ID));
• void rb_define_protected_method(VALUE, const char*, VALUE (*)(ANYARGS), int));
• void rb_define_private_method(VALUE, const char*, VALUE (*)(ANYARGS), int));
• void rb_define_singleton_method(VALUE, const char*, VALUE(*)(ANYARGS), int));
• void rb_define_alloc_func(VALUE, rb_alloc_func_t));
• void rb_undef_alloc_func(VALUE));
• VALUE rb_define_class(const char*,VALUE));
• VALUE rb_define_module(const char*));
• VALUE rb_define_class_under(VALUE, const char*, VALUE));
• VALUE rb_define_module_under(VALUE, const char*));
• void rb_define_variable(const char*,VALUE*));
• void rb_define_virtual_variable(const char*,VALUE(*)(ANYARGS),void(*)(ANYARGS)));
• void rb_define_hooked_variable(const char*,VALUE*,VALUE(*)(ANYARGS),void(*)(ANYARGS)));
• void rb_define_readonly_variable(const char*,const VALUE*));
• void rb_define_const(VALUE,const char*,VALUE));
• void rb_define_global_const(const char*,VALUE));
• void rb_define_method(VALUE,const char*,VALUE(*)(ANYARGS),int));
• (void rb_define_module_function(VALUE,const char*,VALUE(*)(ANYARGS),int));
• void rb_define_global_function(const char*,VALUE(*)(ANYARGS),int));
• void rb_undef_method(VALUE,const char*));
• void rb_define_alias(VALUE,const char*,const char*));
• void rb_define_attr(VALUE,const char*,int,int));
• void rb_global_variable(VALUE*));
• void rb_gc_register_mark_object(VALUE));
• void rb_gc_register_address(VALUE*));
• void rb_gc_unregister_address(VALUE*));

Text segment reductions

Small changes (3144 bytes reduction of the text segment) because this is incremental groundwork and and initial low risk PR.

this branch:

lourens@CarbonX1:~/src/ruby/ruby$ size ruby
   text	   data	    bss	    dec	    hex	filename
3462153	  21056	  71344	3554553	 363cf9	ruby

trunk:

lourens@CarbonX1:~/src/ruby/trunk$ size ruby
   text	   data	    bss	    dec	    hex	filename
3465297	  21056	  71344	3557697	 364941	ruby

Diffs for individual object files: https://www.diffchecker.com/T0GVzX1q

Default text.unlikely section where init functions are moved to:

lourens@CarbonX1:~/src/ruby/ruby$ readelf -S vm.o
There are 34 section headers, starting at offset 0x2a04f8:

Section Headers:
  [Nr] Name              Type             Address           Offset
       Size              EntSize          Flags  Link  Info  Align
  [ 0]                   NULL             0000000000000000  00000000
       0000000000000000  0000000000000000           0     0     0
  [ 1] .text             PROGBITS         0000000000000000  00000040
       000000000001c37f  0000000000000000  AX       0     0     16
  [ 2] .rela.text        RELA             0000000000000000  00114100
       000000000000a7d0  0000000000000018   I      31     1     8
  [ 3] .data             PROGBITS         0000000000000000  0001c3c0
       0000000000000030  0000000000000000  WA       0     0     16
  [ 4] .bss              NOBITS           0000000000000000  0001c400
       00000000000002b0  0000000000000000  WA       0     0     32
  [ 5] .rodata.str1.8    PROGBITS         0000000000000000  0001c400
       0000000000000d6f  0000000000000001 AMS       0     0     8
  [ 6] .text.unlikely    PROGBITS         0000000000000000  0001d16f <<<<<<<<<<<<<<<
       0000000000001aa9  0000000000000000  AX       0     0     1

The relocations for vm.o:

lourens@CarbonX1:~/src/ruby/ruby$ ld -M vm.o
--- truncated ---
.text           0x0000000000400120    0x1de2f
 *(.text.unlikely .text.*_unlikely .text.unlikely.*)
 .text.unlikely
                0x0000000000400120     0x1aa9 vm.o
                0x000000000040038f                rb_define_alloc_func
                0x00000000004003bf                rb_undef_alloc_func
                0x00000000004003c5                Init_Method
                0x0000000000400512                Init_vm_eval
                0x00000000004007a1                Init_eval_method
                0x0000000000400a54                rb_undef
                0x0000000000400c1d                Init_VM
                0x000000000040185f                Init_BareVM
                0x0000000000401b16                Init_vm_objects
                0x0000000000401b61                Init_top_self
 *(.text.exit .text.exit.*)
 *(.text.startup .text.startup.*)
 *(.text.hot .text.hot.*)
 *(.text .stub .text.* .gnu.linkonce.t.*)
 *fill*         0x0000000000401bc9        0x7 
 .text          0x0000000000401bd0    0x1c37f vm.o
                0x00000000004022f0                rb_f_notimplement
                0x0000000000404780                rb_vm_ep_local_ep
                0x00000000004047b0                rb_vm_frame_block_handler
                0x00000000004047e0                rb_vm_cref_new_toplevel
                0x0000000000404870                rb_vm_block_ep_update
                0x0000000000404890                ruby_vm_special_exception_copy
                0x0000000000406960                rb_ec_stack_overflow
                0x00000000004069c0                rb_vm_push_frame
                0x0000000000406b20                rb_vm_pop_frame
                0x0000000000406b30                rb_error_arity
                0x0000000000407180                rb_vm_frame_method_entry
                0x00000000004075e0                rb_vm_rewrite_cref
                0x00000000004076f0                rb_simple_iseq_p
                0x0000000000407700                rb_vm_opt_struct_aref
                0x0000000000407730                rb_vm_opt_struct_aset
                0x0000000000407750                rb_clear_constant_cache
--- truncated ---

I also dabbled with the idea of an INITFUNC macro that also places the Init_xxx functions into a text.init section as the kernel does for a possible future optimization of stripping out ELF sections for setup / init specific functions. I don't think that makes sense for now and possibly only interesting for mruby or embedded.

Possible next units of work

Cold code specific

• Incrementally PR corner case error handling functions such as rb_bug from https://github.com/ruby/ruby/pull/1922
• Ditto for generic error handling functions (rb_raise and friends) from https://github.com/ruby/ruby/pull/1922
• Class specific error handling functions (load errors, encoding errors in the IO module, sys errors etc.) from https://github.com/ruby/ruby/pull/1922
• GCC 5+ also supports cold labels , which I took a stab with in the bloated https://github.com/ruby/ruby/pull/1922

TLB (translation lookaside buffer) specific

• Further ITLB overhead investigation
• Ruby binaries built with O3 and debug symbols come in at just short of 18MB, or roughly 9 hugepages on linux. PHP core developers were able to squeeze a few % by remapping code to hugepages on supported systems - http://developers-club.com/posts/270685/ . Implementation here

Bytecode specific

• The Intel Tracing Task API is very well suited for the instruction sequences YARV generates and to infer better per instruction CPU utilization and identify any stalls (frontend, backend, branches etc.) to drive further work.

[Eregon (Benoit Daloze)]

What is "original chunky PR" VS "then trunk"?
Which one is original and which one with your patch?
The first one seems better.

[methodmissing (Lourens Naudé)]

Eregon (Benoit Daloze) wrote:

What is "original chunky PR" VS "then trunk"?
Which one is original and which one with your patch?
The first one seems better.

First one is from the changeset in https://github.com/ruby/ruby/pull/1922, but it's gotten too large to review, hence the split into smaller incremental changes. Sorry for that confusion.

[shyouhei (Shyouhei Urabe)]

Interesting.

Re: label attributes. JFYI I once tried them https://github.com/ruby/ruby/pull/1805/files
(answer, bitblt, and all the trace_* instructions are marked cold.)
It did change generated binary to arrange branches, but I saw no performance gains.
Maybe this was because CPUs are much smarter than human beings to detect which branch is hot.

[normalperson (Eric Wong)]

Thank you for taking the time to do this!

The GCC specific cold function attribute works in the following way (from GCC docs):

Since it's gcc (and clang); can we just use something like what
Linux uses:

#define __cold attribute((cold))

Instead of our ugly convention of: COLD( required prototype goes here );

It would allow us to be more DRY by avoiding prototypes for
static functions.

By declaring a function as cold when defined we get the following benefits:

• No-op on platforms that does not support the attribute
• Size optimization of cold functions with a smaller footprint in the instruction cache

Very much agreed. I've always hated the icache footprint from -O3
since so much of our code is rarely executed.

Another benefit is it helps document code paths as to which ones
are most critical :>

Extension APIs flagged as cold

These are and should typically only be called on extension init, and thus safe to optimize for size as well.

• void rb_define_method(VALUE,const char*,VALUE(*)(ANYARGS),int));

Does this affect startup performance? (with --disable=gems)

• Ruby binaries built with O3 and debug symbols come in at
  just short of 18MB, or roughly 9 hugepages on linux. PHP core
  developers were able to squeeze a few % by remapping code to
  hugepages on supported systems -
  http://developers-club.com/posts/270685/ . Implementation
  here

Cool. While THP is a disaster for CoW and anonymous mappings;
it makes perfect sense for large read-only mappings

Now, the question is; shouldn't this be done in ld-linux.so
(part of glibc) instead?

[methodmissing (Lourens Naudé)]

normalperson (Eric Wong) wrote:

Thank you for taking the time to do this!

The GCC specific cold function attribute works in the following way (from GCC docs):

Since it's gcc (and clang); can we just use something like what
Linux uses:

#define __cold attribute((cold))

Instead of our ugly convention of: COLD( required prototype goes here );

Initial pass had that, but I decided to line up with recommendations from the guidelines. Not great for human parsing, especially when nested with NORETURN etc.

It would allow us to be more DRY by avoiding prototypes for
static functions.

By declaring a function as cold when defined we get the following benefits:

• No-op on platforms that does not support the attribute
• Size optimization of cold functions with a smaller footprint in the instruction cache

Very much agreed. I've always hated the icache footprint from -O3
since so much of our code is rarely executed.

Another benefit is it helps document code paths as to which ones
are most critical :>

Extension APIs flagged as cold

These are and should typically only be called on extension init, and thus safe to optimize for size as well.

• void rb_define_method(VALUE,const char*,VALUE(*)(ANYARGS),int));

Does this affect startup performance? (with --disable=gems)

Great point, I'll investigate.

• Ruby binaries built with O3 and debug symbols come in at
  just short of 18MB, or roughly 9 hugepages on linux. PHP core
  developers were able to squeeze a few % by remapping code to
  hugepages on supported systems -
  http://developers-club.com/posts/270685/ . Implementation
  here

Cool. While THP is a disaster for CoW and anonymous mappings;
it makes perfect sense for large read-only mappings

Yeah, does terrible things - the way this would work is reserving 20MB worth more or less with /proc/sys/vm/nr_hugepages (1 value of 10 in there) just for the ruby binary.

Now, the question is; shouldn't this be done in ld-linux.so
(part of glibc) instead?

Possible, but there's already https://github.com/libhugetlbfs/libhugetlbfs (more specifically https://github.com/libhugetlbfs/libhugetlbfs/blob/master/HOWTO#L370 ) Maybe an --enable-libhugetlbfs config option. That also exposes an API for mapping bytecode to huge pages, if it's possible to have a reserved heap for iseqs. Anyways, drifting off topic ...

[ko1 (Koichi Sasada)]

I agree to introduce COLD attribute.

---

TLB (translation lookaside buffer) specific

Do PHP people specify THP with DWARF knowledge?

[Hanmac (Hans Mackowiak)]

what happens when i would call such cold function outside of Init_xxx ?

what functions in my own binding should be using cold?
like for example i have a own _attr_method function that mimic a attribute by setting a Get/Set function

[methodmissing (Lourens Naudé)]

ko1 (Koichi Sasada) wrote:

I agree to introduce COLD attribute.

I was wondering about Eric's suggestion about the convention for using it though. I like the Kernel style of COLDFUNC void some_func() or COLD void some_func() more than this style we have now enforced in the contributor docs:

COLDFUNC(void Init_Array(void));
void
Init_Array(void)

Also thoughts on an explicit INITFUNC macro for extension authors + documentation in the extensions guide as a forward looking contract for init functions?

---

TLB (translation lookaside buffer) specific

Do PHP people specify THP with DWARF knowledge?

THP turned off, explicitly maps the read only sections to some of a pool of pre-allocated huge pages - around 10 x 2MB for ruby to have some buffer. as binaries with O3 and debug symbols are weighing in @ 18MB now. I have a work in progress branch with CFLAGS -B /usr/share/libhugetlbfs, -Wl,--hugetlbfs-align but unfortunately having issues with the -B flag + gcc 7.3 (bug in Bionic). I got likwid up and running yesterday (master supports recent kabylakes) and have ballbark figures of optcarrot being around 5% Instruction TLB bound, with a miss overhead estimate of around 30 cycles.

For this COLD attribute change, I still need to:

• Assert no negative effect on startup performance (with --disable=gems)
• Another pass through likwid with the icache group (and pin to a specific CPU core to reduce noise) with optcarrot
• Ditto for Intel VTune
• Add the results to the original PR

The goal with this change is to introduce a mechanism for better code layout, then follow up with further incremental work to reduce the instruction cache footprint and improve branch prediction of callsites for rb_bug and other super rare invocations.

[methodmissing (Lourens Naudé)]

Hanmac (Hans Mackowiak) wrote:

what happens when i would call such cold function outside of Init_xxx ?

I considered primarily only core for this change and carefully looked @ usage of the extension API in Init_xxx functions, but for sure there's going to be edges in the wild with other extensions. I only chose to override the public API functions that you won't call much in a hot path either (or shouldn't). Also optimized for size VS performance, sometimes a function with smaller code size can execute faster than an optimized one.

what functions in my own binding should be using cold?
like for example i have a own _attr_method function that mimic a attribute by setting a Get/Set function

I can document likely candidates (what to look for, to consider - most would have a strong system specific or exceptions error path, depending on what's being wrapped) in the extensions guide as part of this change, if that works ...

[naruse (Yui NARUSE)]

methodmissing (Lourens Naudé) wrote:

ko1 (Koichi Sasada) wrote:

I agree to introduce COLD attribute.

I was wondering about Eric's suggestion about the convention for using it though. I like the Kernel style of COLDFUNC void some_func() or COLD void some_func() more than this style we have now enforced in the contributor docs:

COLDFUNC(void Init_Array(void));
void
Init_Array(void)

It uses function style macro because some function attribute of MSVC are valid only if written as suffix.
Therefore about coldfunc, just constant style is ok.

Follwing patch or just use new macro other than RUBY_FUNC_ATTRIBUTE..

diff --git a/configure.ac b/configure.ac
index a48eda1532..a6cd0b4928 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1302,6 +1302,7 @@ AS_IF([test "$rb_cv_have_alignof" != no], [

 RUBY_FUNC_ATTRIBUTE(__const__, CONSTFUNC)
 RUBY_FUNC_ATTRIBUTE(__pure__, PUREFUNC)
+RUBY_FUNC_ATTRIBUTE(__cold__, COLDFUNC)
 RUBY_FUNC_ATTRIBUTE(__noreturn__, NORETURN)
 RUBY_FUNC_ATTRIBUTE(__deprecated__, DEPRECATED)
 RUBY_FUNC_ATTRIBUTE(__deprecated__("by "@%:@n), DEPRECATED_BY(n,x), rb_cv_func_deprecated_by)
diff --git a/tool/m4/ruby_decl_attribute.m4 b/tool/m4/ruby_decl_attribute.m4
index f15947c0ab..87f3242a96 100644
--- a/tool/m4/ruby_decl_attribute.m4
+++ b/tool/m4/ruby_decl_attribute.m4
@@ -35,6 +35,10 @@ done
 ])])
 AS_IF([test "$rbcv" != x], [
     RUBY_DEFINE_IF(m4_ifval([$4],[${rbcv_cond}]), attrib[](attrib_params)[], $rbcv)
+    AS_CASE(["$mac"],
+    ["__attribute__ ((attrib_code)) x"|"__declspec(attrib_code) x"], [
+        RUBY_DEFINE_IF(m4_ifval([$4],[${rbcv_cond}]), attrib[_PREFIX], ${rbcv% x})
+    ])
 ])
 m4_ifval([$4], [unset rbcv_cond]) dnl
 m4_popdef([attrib_params])dnl

[methodmissing (Lourens Naudé)]

naruse (Yui NARUSE) wrote:

methodmissing (Lourens Naudé) wrote:

ko1 (Koichi Sasada) wrote:

I agree to introduce COLD attribute.

I was wondering about Eric's suggestion about the convention for using it though. I like the Kernel style of COLDFUNC void some_func() or COLD void some_func() more than this style we have now enforced in the contributor docs:

COLDFUNC(void Init_Array(void));
void
Init_Array(void)

It uses function style macro because some function attribute of MSVC are valid only if written as suffix.
Therefore about coldfunc, just constant style is ok.

Thanks for clarifying the context there. I looked @ MSVC attributes / annotations and cold (or anything similar) is not supported, thus for cold and hot attributes constant style as prefix only should be fine.

Any preferences on these for constant style attribute annotation?

• COLD - clearly expressed, but not namespaced and there's a possibility for bindings already having such a macro defined
• COLDFUNC - as above, but less chance of collision
• RB_COLD - as above, but aligns better with existing macros (RB_ prefix)
• FUNC_COLDCALL - for alignment with FUNC_FASTCALL (although very much specific to VM code paths only, and MSVC specific)

Follwing patch or just use new macro other than RUBY_FUNC_ATTRIBUTE..

diff --git a/configure.ac b/configure.ac
index a48eda1532..a6cd0b4928 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1302,6 +1302,7 @@ AS_IF([test "$rb_cv_have_alignof" != no], [

 RUBY_FUNC_ATTRIBUTE(__const__, CONSTFUNC)
 RUBY_FUNC_ATTRIBUTE(__pure__, PUREFUNC)
+RUBY_FUNC_ATTRIBUTE(__cold__, COLDFUNC)
 RUBY_FUNC_ATTRIBUTE(__noreturn__, NORETURN)
 RUBY_FUNC_ATTRIBUTE(__deprecated__, DEPRECATED)
 RUBY_FUNC_ATTRIBUTE(__deprecated__("by "@%:@n), DEPRECATED_BY(n,x), rb_cv_func_deprecated_by)
diff --git a/tool/m4/ruby_decl_attribute.m4 b/tool/m4/ruby_decl_attribute.m4
index f15947c0ab..87f3242a96 100644
--- a/tool/m4/ruby_decl_attribute.m4
+++ b/tool/m4/ruby_decl_attribute.m4
@@ -35,6 +35,10 @@ done
 ])])
 AS_IF([test "$rbcv" != x], [
     RUBY_DEFINE_IF(m4_ifval([$4],[${rbcv_cond}]), attrib[](attrib_params)[], $rbcv)
+    AS_CASE(["$mac"],
+    ["__attribute__ ((attrib_code)) x"|"__declspec(attrib_code) x"], [
+        RUBY_DEFINE_IF(m4_ifval([$4],[${rbcv_cond}]), attrib[_PREFIX], ${rbcv% x})
+    ])
 ])
 m4_ifval([$4], [unset rbcv_cond]) dnl
 m4_popdef([attrib_params])dnl

[methodmissing (Lourens Naudé)]

ko1 (Koichi Sasada) wrote:

I agree to introduce COLD attribute.

---

TLB (translation lookaside buffer) specific

Do PHP people specify THP with DWARF knowledge?

Somewhat off topic, but fits with the general direction here.

I have a proof of concept going with mapping the text section to hugepages after a few evenings of interesting segfaults. It uses a small custom linker script and an API that first tries to map text with:

• MAP_HUGETLB - explicit request, requires hubgetlbfs mount and pages reserved explicitly ahead of time, will fail if that's not true
• MADV_HUGEPAGE - fallback option, implicit request, kernel will map it implicit if not aligned to hugepage boundary, or right away if aligned to hugepage boundary (I implemented with the 2MB alignment for my system). Requires a kernel compiled with THP support (most are) and THP enabled (likewise)

It's easy to check for the support of either and also very easy to back out of the hugepage mapping attempt and just fallback to 4k pages.

The text section of trunk with -O3 is around 3.3MB, meaning it maps to 1 x 2MB huge page and then the rest to 4k standard pages. What's interesting here is the possibility of NOT mapping all of the text section, but only a more concise hot section into a single hugepage, effectively removing all ITLB overhead for the hot code paths. And further prune down the text footprint of rarely invoked functions with COLDFUNC. Anyways, just some thoughts.

[normalperson (Eric Wong)]

[e-mail] wrote:

• MADV_HUGEPAGE - fallback option, implicit request, kernel
  will map it implicit if not aligned to hugepage boundary, or
  right away if aligned to hugepage boundary (I implemented with
  the 2MB alignment for my system). Requires a kernel compiled
  with THP support (most are) and THP enabled (likewise)

Crap, I think that conflicts with the usage of
PR_SET_THP_DISABLE (for CoW-friendliness) since r63253 in trunk.
MAP_HUGETLB will still work, though.

[methodmissing (Lourens Naudé)]

normalperson (Eric Wong) wrote:

[e-mail] wrote:

• MADV_HUGEPAGE - fallback option, implicit request, kernel
  will map it implicit if not aligned to hugepage boundary, or
  right away if aligned to hugepage boundary (I implemented with
  the 2MB alignment for my system). Requires a kernel compiled
  with THP support (most are) and THP enabled (likewise)

Crap, I think that conflicts with the usage of
PR_SET_THP_DISABLE (for CoW-friendliness) since r63253 in trunk.
MAP_HUGETLB will still work, though.

Yes, explains behaviour observed through smaps - correct, MAP_HUGETLB works. Will clean it up during the week and submit as a new issue.

[ko1 (Koichi Sasada)]

I agree to introduce cold attribute (I have no idea about the naming).

rb_bug or rb_warn (etc) should be cold functions because they should not be called.

However, I'm not sure rb_define_... and so on because it can affect startup time for big Ruby application. We need to specify with benchmark results.

[methodmissing (Lourens Naudé)]

ko1 (Koichi Sasada) wrote:

I agree to introduce cold attribute (I have no idea about the naming).

rb_bug or rb_warn (etc) should be cold functions because they should not be called.

However, I'm not sure rb_define_... and so on because it can affect startup time for big Ruby application. We need to specify with benchmark results.

Yes, I agree - in retrospect rb_define functions would affect startup time, especially for very large Rails applications. I was waiting on further input from core for guidance as it's very easy to fall into a trap and go too wide with cold attributes. I've been using clang a lot more lately as well and think the following scope with proper benchmark qualification could work well:

• Support clang and gcc versions with cold attr support (I did not see any support for MSVC but need to confirm again)
• rb_bug and rb_warn (1 first class internal and 1 first class user API call)
• Possibly rb_memerror and a few similar extreme edge case ones that cannot be used for flow control
• That way there's also a better chance of slight branch prediction improvements along with code relocation

Does that seem reasonable as a unit of work to you?

[ko1 (Koichi Sasada)]

Does that seem reasonable as a unit of work to you?

Perfect!

Note that we will release ruby 2.6 in Dec. If you finish (3) "Possibly rb_memerror...", it is easy to introduce. We can continue further improvement on next release.

[methodmissing (Lourens Naudé)]

ko1 (Koichi Sasada) wrote:

Does that seem reasonable as a unit of work to you?

Perfect!

Note that we will release ruby 2.6 in Dec. If you finish (3) "Possibly rb_memerror...", it is easy to introduce. We can continue further improvement on next release.

I added some investigation and conclusions with gcc and clang to the reduced scope PR https://github.com/ruby/ruby/pull/2005

[methodmissing (Lourens Naudé)]

methodmissing (Lourens Naudé) wrote:

ko1 (Koichi Sasada) wrote:

Does that seem reasonable as a unit of work to you?

Perfect!

Note that we will release ruby 2.6 in Dec. If you finish (3) "Possibly rb_memerror...", it is easy to introduce. We can continue further improvement on next release.

I added some investigation and conclusions with gcc and clang to the reduced scope PR https://github.com/ruby/ruby/pull/2005

I'm having a hard time getting MSVC to pass for rb_memerror https://ci.appveyor.com/project/ruby/ruby/builds/20571215/job/wc9ha9eg36xjiv70 with error c:\projects\ruby\include\ruby/intern.h(482) : error C4028: formal parameter 1 different from declaration (https://github.com/ruby/ruby/pull/2005)

• Declarations https://github.com/ruby/ruby/pull/2005/files#diff-d25389b5dda13be5e80e89f60e1cc716R482 and https://github.com/ruby/ruby/blob/18865dc5d69e7931f18ccadb62bd1a8264836c80/gc.c#L7882-L7883 looks aligned to me, but doesn't seem to like the nested NORETURN and COLDFUNC
• It's possible to conditionally define the attribute, but having excessive ifdefs for MSVC in intern.h for public API isn't great and bad for maintenance

Any thoughts much appreciated.

[methodmissing (Lourens Naudé)]

methodmissing (Lourens Naudé) wrote:

methodmissing (Lourens Naudé) wrote:

ko1 (Koichi Sasada) wrote:

Does that seem reasonable as a unit of work to you?

Perfect!

Note that we will release ruby 2.6 in Dec. If you finish (3) "Possibly rb_memerror...", it is easy to introduce. We can continue further improvement on next release.

I added some investigation and conclusions with gcc and clang to the reduced scope PR https://github.com/ruby/ruby/pull/2005

I'm having a hard time getting MSVC to pass for rb_memerror https://ci.appveyor.com/project/ruby/ruby/builds/20571215/job/wc9ha9eg36xjiv70 with error c:\projects\ruby\include\ruby/intern.h(482) : error C4028: formal parameter 1 different from declaration (https://github.com/ruby/ruby/pull/2005)

• Declarations https://github.com/ruby/ruby/pull/2005/files#diff-d25389b5dda13be5e80e89f60e1cc716R482 and https://github.com/ruby/ruby/blob/18865dc5d69e7931f18ccadb62bd1a8264836c80/gc.c#L7882-L7883 looks aligned to me, but doesn't seem to like the nested NORETURN and COLDFUNC
• It's possible to conditionally define the attribute, but having excessive ifdefs for MSVC in intern.h for public API isn't great and bad for maintenance

Any thoughts much appreciated.

Fallback to a definition in defines.h for clang and GCC 4.3.0+ only as MSVC didn't like the NORETURN + COLDFUNC combo for rb_memerror.

https://github.com/ruby/ruby/pull/2005/files#diff-b6f26affdb29910802b4d97a901fe689R92

[ko1 (Koichi Sasada)]

methodmissing (Lourens Naudé) wrote:

https://github.com/ruby/ruby/pull/2005/files#diff-b6f26affdb29910802b4d97a901fe689R92

:+1:

[naruse (Yui NARUSE)]

r66228 merged https://github.com/ruby/ruby/pull/2005/files#diff-b6f26affdb29910802b4d97a901fe689R92, thanks!

[hsbt (Hiroshi SHIBATA)]

• Status changed from Open to Assigned