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methodmissing committed Apr 22, 2009
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h1. MRI Instrumentation

There's a lot of black magic and speculation as to the inner workings of the Ruby VM.This is an experiment with MRI internals that :

* is supported on OS X Leopard, Solaris and any other dtrace enabled environment
* is unobtrusive - use whichever Ruby 18 version you already have installed
* expects probe definitions to be structured as YAML for possible porting to other dynamic tracing frameworks

h2. How the dtrace PID provider works

A set of C level probes is spawned for the lifetime of a given command or existing process.When the process dies, the probe's is unset.You don't have to recompile or relink - it just works.

h2. Why bother ?

A dtrace environment is available to most ruby developers, offers fast dynamic runtime instrumentation and the D language is well suited for presenting data through different visual strategies.

This package is primarily aimed at framework style development where deep instrumentation may yield significant insight into potential performance hotspots.

h2. Installation

<pre>
<code>
git clone git://github.com/methodmissing/mri_instrumentation.git
cd mri_instrumentation
ruby bin/instrument --help
</code>
</pre> _

h2. Probe definitions:

Through YAML everyone can be a C buff :

<pre>
<code>
rb_clear_cache:
rb_clear_cache_by_id:
rb_clear_cache_by_class:
</code>
</pre>

Probes can also define arguments and expected return values :

<pre>
<code>
rb_clear_cache_by_id:
args:
- int: 'Id'
return: void
</code>
</pre>

Although support's built in for coersion etc. I've found working with void returns and pointer arguments to be somewhat problematic, hence the barebones argumentless definitions.It'll be fixed real soon.

h1. Usage examples

Early days, but one of the following instrumentation modes is supported :

* attach to a running PID
* run / spawn a new ruby process

Various different profiling strategies would be supported, but we're shipping with a conservative calltime strategy in this initial release.Expect execution flow, stack traces on error conditions etc. as potential future options.

<pre>
<code>
213-138-231-176:mri_instrumentation lourens$ ruby bin/instrument --help
Usage: instrument [OPTIONS] probe1 probe2 probe3
MRI instrumentation with the dtrace pid provider
-pid=[val] The process identifier (PID) to attach to
Default: 0
-cmd=[val] The command to run
Default:
-strategy=[val] The desired profiling strategy
Default: calltime
-h, --help Show this help message.
</code>
</pre>

h2. MRI's internal method cache

<pre>
<code>
213-138-231-176:mri_instrumentation lourens$ ruby bin/instrument -c /Users/lourens/projects/superbreak_app/script/console cache
./bin/../lib/mri/instrumentation/runner/base.rb:86: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
Loading development environment (Rails 2.3.2)
/Users/lourens/projects/superbreak_app/vendor/rails/railties/lib/commands/console.rb:45: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
Tracing... Hit Ctrl-C to end.
>> exit

Count,
Probe COUNT
rb_clear_cache 43
rb_clear_cache_by_class 89
rb_clear_cache_by_id 3266

Exclusive function elapsed times (us),
Probe TOTAL
rb_clear_cache 258
rb_clear_cache_by_class 691
rb_clear_cache_by_id 15553

Inclusive function elapsed times (us),
Probe TOTAL
rb_clear_cache 258
rb_clear_cache_by_class 691
rb_clear_cache_by_id 15553
</code>
</pre>

h2. What blocks have been up to

<pre>
<code>
213-138-231-176:mri_instrumentation lourens$ ruby bin/instrument -c /Users/lourens/projects/superbreak_app/script/console block
./bin/../lib/mri/instrumentation/runner/base.rb:86: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
Loading development environment (Rails 2.3.2)
/Users/lourens/projects/superbreak_app/vendor/rails/railties/lib/commands/console.rb:45: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
Tracing... Hit Ctrl-C to end.
>> exit

Count,
Probe COUNT
yield_under 1
yield_under_i 1
blk_copy_prev 11
blk_free 12
blk_dup 20
blk_mark 58
block_pass 62
rb_yield 862
rb_need_block 882
rb_yield_0 882
rb_block_given_p 1641

Exclusive function elapsed times (us),
Probe TOTAL
yield_under_i 17
yield_under 26
blk_copy_prev 70
blk_free 73
blk_dup 102
blk_mark 635
block_pass 1187
rb_block_given_p 6320
rb_yield 15681
rb_need_block 18327
rb_yield_0 36787

Inclusive function elapsed times (us),
Probe TOTAL
yield_under_i 57
blk_copy_prev 70
blk_free 73
yield_under 83
blk_dup 102
blk_mark 718
block_pass 1639
rb_block_given_p 6320
rb_need_block 21705
rb_yield_0 87886
rb_yield 98256
</code>
</pre>

h1. Garbage Collection

<pre>
<code>
213-138-231-176:mri_instrumentation lourens$ ruby bin/instrument -c /Users/lourens/projects/superbreak_app/script/console gc
./bin/../lib/mri/instrumentation/runner/base.rb:86: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
Tracing... Hit Ctrl-C to end.
Loading development environment (Rails 2.3.2)
/Users/lourens/projects/superbreak_app/vendor/rails/railties/lib/commands/console.rb:45: warning: Insecure world writable dir /Users/lourens in PATH, mode 040753
>> exit

Count,
Probe COUNT
rb_gc_unregister_address 1
add_heap 4
free_unused_heaps 4
garbage_collect 4
rb_gc_mark_locations 5
mark_locations_array 9
rb_mark_tbl 9
rb_global_variable 22
mark_hash 23
rb_gc_register_address 23
sweep_source_filename 91
rb_data_object_alloc 114
rb_source_filename 129
rb_gc_mark_frame 163
rb_gc_mark_maybe 222
rb_gc_mark 575
ruby_stack_check 601
stack_end_address 605
mark_keyvalue 891
ruby_xcalloc 1361
ruby_xfree 1596
ruby_xrealloc 3053
mark_tbl 3701
rb_gc_force_recycle 6158
mark_entry 15342
ruby_xmalloc 45903
gc_mark_children 53783
gc_mark 74469
mark_source_filename 93431
rb_newobj 96586

Exclusive function elapsed times (us),
Probe TOTAL
rb_gc_unregister_address 4
free_unused_heaps 19
rb_gc_mark_locations 23
rb_mark_tbl 34
rb_global_variable 91
mark_locations_array 136
sweep_source_filename 308
rb_gc_register_address 407
rb_gc_mark_frame 608
rb_gc_mark_maybe 710
rb_gc_mark 2003
rb_data_object_alloc 2015
rb_source_filename 2050
stack_end_address 2457
add_heap 2805
ruby_xfree 6334
ruby_xrealloc 11883
ruby_stack_check 12954
mark_hash 14022
rb_gc_force_recycle 21856
ruby_xcalloc 23749
mark_keyvalue 44226
ruby_xmalloc 173719
mark_tbl 199721
gc_mark 277730
mark_source_filename 332414
rb_newobj 341314
mark_entry 393127
gc_mark_children 3122918

Inclusive function elapsed times (us),
Probe TOTAL
rb_gc_unregister_address 4
free_unused_heaps 19
rb_gc_mark_locations 23
rb_mark_tbl 34
rb_global_variable 91
sweep_source_filename 308
rb_gc_register_address 489
mark_locations_array 500
rb_gc_mark_frame 608
rb_gc_mark_maybe 710
rb_gc_mark 2003
rb_data_object_alloc 2437
rb_source_filename 2456
stack_end_address 2457
add_heap 2805
ruby_xfree 6334
ruby_xrealloc 11883
ruby_stack_check 15396
rb_gc_force_recycle 21856
ruby_xcalloc 28800
mark_keyvalue 92162
mark_hash 106184
ruby_xmalloc 173719
gc_mark 291686
mark_source_filename 332414
rb_newobj 341314
mark_tbl 1905278
mark_entry 4311987
gc_mark_children 18471501
</code>
</pre>

Thanks for reading - on holidays for the next 3 weeks, expect updates to be sporadic and patchy during that time.

(c) 2009 Lourens Naudé (methodmissing)

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