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Since it's been quite a while since I've written C code, *and* I
haven't done any significant hacking on the VM itself in years, it's
quite likely that I haven't done things in 100% proper style. Or
my co-collaborators Dustin Sallings (CouchBase) or Michal Ptaszek
(Erlang Solutions). My intent for this patch is to start discussion
and review of DTrace support for consideration for the R15 release.
For additional background on the motivation for this work, please
see the slides for the presentation at the Erlang User Conference 2011
in Stockholm:
https://www.erlang-factory.com/upload/presentations/462/euc2011-draft2.pdf
Changes relative to dtrace-review2 branch:
* Fix errors in OTP test suite 'kernel' file_SUITE
* Fix errors in OTP test suite 'kernel' prim_file_SUITE
* Fix bad pointer bug in efile_drv.c flush_write()
* Move the DTrace material from the top of `README.md` into a
new file, `README.dtrace.md`
Changes since last push to GitHub (relative to commit 5828a4fb28, which
was the former `dtrace-review1` branch):
* Rebased onto 14 Nov 2011's "master" branch
* Recent changes to the async task queuing mechanism means that
the async worker queue length is not available. A bogus value
of -1 is hard-coded until there's a good way to peek into the
new queue structure and find the queue length.
* Small fixes based on review comments by Mikael Pettersson,
Andrew Thompson, and Andreas Schultz.
Add autoconf support: use "./configure --enable-dtrace" on all supported
platforms:
* OS X Snow Leopard or later
* Solaris 10 or OpenSolaris
* Linux, via SystemTap's DTrace compatibility packages
* FreeBSD 9.0RC1. FreeBSD 8 and earlier do not have support
for USDT, DTrace's User-land Statically Defined Tracing.
See the file `erts/emulator/beam/erlang_dtrace.d` for the definition
of all DTrace probes in the virtual machine so far.
Example D scripts can be found in `lib/dtrace/examples`. Note that if
you see the error message `{name of probe} does not match any probes`,
then there is no Erlang VM process + DTrace probes running. To fix,
start a DTrace-enabled VM or remove `-q` from the `dtrace` command line.
The `lib/dtrace` directory contains a small code-only OTP application
that contains code that allows Erlang code to trigger a DTrace probe.
Dynamic creation & deletion of DTrace probes is not currently
supported, so the `dtrace:p()` function is hacked to allow a variable
number of arguments (up to four integers and up to four strings) to be
used. See the comments at the top of `lib/dtrace/src/dtrace.c` for
more detail.
One feature that may be controversial is the notion I've introduced
of a special process dictionary key that can be used by Erlang code to
tag I/O operations for an application-specific purpose. Right now,
that tag's name is `dtrace_utag`. The dictionary keys used by `sys`
and other modules start with a dollar sign. Perhaps there is some
convention (but not a dollar sign?) that this tag should use?
The purpose of the process dictionary key is to allow the tag to
be included in trace messages, e.g. for file I/O, without changing the
API of the `file.erl` module's functions. For example, here's a use
of the tag when calling the `file:rename/2` function:
(bar@sbb2)1> put(dtrace_utag, "GGOOOAAALL!!!!!").
undefined
(bar@sbb2)2> dtrace:init().
ok
%% Now start both the `user-probe.d` and `efile_drv.d` D scripts
%% found in the `lib/dtrace/examples` directory.
(bar@sbb2)3> dtrace:p(7, 8, 9, "one", "four").
true
%% The output from the `user-probe.d` script:
<0.40.0> GGOOOAAALL!!!!! 7 8 9 0 'one' 'four' '' ''
(bar@sbb2)4> file:rename("old-name", "new-name").
{error,enoent}
%% The output from the `efile_drv.d` script:
async I/O pool port #Port<0.59> queue len 1
async I/O pool port #Port<0.59> queue len 0
efile_drv enter tag={1,110} user tag GGOOOAAALL!!!!! | RENAME (12) | args: old-name new-name , 0 0 (port #Port<0.59>)
async I/O worker tag={1,110} | RENAME (12) | efile_drv-int_entry
async I/O worker tag={1,110} | RENAME (12) | efile_drv-int_return
efile_drv return tag={1,110} user tag GGOOOAAALL!!!!! | RENAME (12) | errno 2
I'm not exactly happy with this choice of tagging, namely using
`put(dtrace_utag, Tag::list())`. But this is an experiment, so
we'll see how it goes. I can't imagine changing the API for
all file.erl functions in order pass the tag explicitly.
Some modules have some extensive (ab)use of the C preprocessor to
reduce the amount of #ifdefs that clutter the code. In several places,
I have not #ifdef'ed automatic variables because of clutter. For the
same reason, there are a handful of cases where I added DTrace-related
members to a struct definition without an #ifdef. I feel that the
result is easier to read than earlier drafts where I did use many more
`https://github.com/slfritchie/otp/tree/dtrace-experiment+michal2` if
you're curious.) I expect there may be some debate about whether the
bloat of the affected structs is worthwhile. I erred on adding stuff
to structs, especially in the efile_drv.c driver, not having a full
grasp on what was thread-safe and what was not ... so I erred on the
side of caution.
The efile_drv.c has a work-around for a crazy GCC optimization bug.
Thank goodness for Google, I dunno how I would've found a work-around
for this silly thing. Many thanks to Trond Norbye for writing clearly
about the problem in a membase Git repo commit message.
/*
* A note on probe naming: if "__" appears in a provider probe
* definition, then two things happen during compilation:
*
* 1. The "__" will turn into a hypen, "-", for the probe name.
* 2. The "__" will turn into a single underscore, "_", for the
* macro names and function definitions that the compiler and
* C developers will see.
*
* We'll try to use the following naming convention. We're a bit
* limited because, as a USDT probe, we can only specify the 4th part
* of the probe name, e.g. erlang*:::mumble. The 2nd part of the
* probe name is always going to be "beam" or "beam.smp", and the 3rd
* part of the probe name will always be the name of the function
* that's calling the probe.
*
* So, all probes will be have names defined in this file using the
* convention category__name or category__sub_category__name. This
* will translate to probe names of category-name or
* category-sub_category-name.
*
* Each of "category", "sub_category", and "name" may have underscores
* but may not have hyphens.
*/
Add tentative support for sequential tracing sending, queueing, and
receiving a message. I don't believe I've fully covered all the major
places where it would be useful to have the sequential trace token info
in a probe -- guidance from the OTP team would be helpful, if there's
time to do that kind of review.
Add global variable `erts_this_node_sysname`.
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The ethread atomics API now also provide double word size atomics.
Double word size atomics are implemented using native atomic
instructions on x86 (when the cmpxchg8b instruction is available)
and on x86_64 (when the cmpxchg16b instruction is available). On
other hardware where 32-bit atomics or word size atomics are
available, an optimized fallback is used; otherwise, a spinlock,
or a mutex based fallback is used.
The ethread library now performs runtime tests for presence of
hardware features, such as for example SSE2 instructions, instead
of requiring this to be determined at compile time.
There are now functions implementing each atomic operation with the
following implied memory barrier semantics: none, read, write,
acquire, release, and full. Some of the operation-barrier
combinations aren't especially useful. But instead of filtering
useful ones out, and potentially miss a useful one, we implement
them all.
A much smaller set of functionality for native atomics are required
to be implemented than before. More or less only cmpxchg and a
membar macro are required to be implemented for each atomic size.
Other functions will automatically be constructed from these. It is,
of course, often wise to implement more that this if possible from a
performance perspective.
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Building in a source tree without prebuilt platform independent
build results failed on the SSL examples when cross building.
This has been solved by not building the SSL examples during a
cross build.
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Large parts of the ethread library have been rewritten. The
ethread library is an Erlang runtime system internal, portable
thread library used by the runtime system itself.
Most notable improvement is a reader optimized rwlock
implementation which dramatically improve the performance of
read-lock/read-unlock operations on multi processor systems by
avoiding ping-ponging of the rwlock cache lines. The reader
optimized rwlock implementation is used by miscellaneous
rwlocks in the runtime system that are known to be read-locked
frequently, and can be enabled on ETS tables by passing the
`{read_concurrency, true}' option upon table creation. See the
documentation of `ets:new/2' for more information.
The ethread library can now also use the libatomic_ops library
for atomic memory accesses. This makes it possible for the
Erlang runtime system to utilize optimized atomic operations
on more platforms than before. Use the
`--with-libatomic_ops=PATH' configure command line argument
when specifying where the libatomic_ops installation is
located. The libatomic_ops library can be downloaded from:
http://www.hpl.hp.com/research/linux/atomic_ops/
The changed API of the ethread library has also caused
modifications in the Erlang runtime system. Preparations for
the to come "delayed deallocation" feature has also been done
since it depends on the ethread library.
Note: When building for x86, the ethread library will now use
instructions that first appeared on the pentium 4 processor. If
you want the runtime system to be compatible with older
processors (back to 486) you need to pass the
`--enable-ethread-pre-pentium4-compatibility' configure command
line argument when configuring the system.
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If FOP is not found create PDF files with fakefop script.
Signed-off-by: Tuncer Ayaz <[email protected]>
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* pan/otp_8332_halfword:
Teach testcase in driver_suite the new prototype for driver_async
wx: Correct usage of driver callbacks from wx thread
Adopt the new (R13B04) Nif functionality to the halfword codebase
Support monitoring and demonitoring from driver threads
Fix further test-suite problems
Correct the VM to work for more test suites
Teach {wordsize,internal|external} to system_info/1
Make tracing and distribution work
Turn on instruction packing in the loader and virtual machine
Add the BeamInstr data type for loaded BEAM code
Fix the BEAM dissambler for the half-word emulator
Store pointers to heap data in 32-bit words
Add a custom mmap wrapper to force heaps into the lower address range
Fit all heap data into the 32-bit address range
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The INSTALL.md, INSTALL-CROSS.md, and INSTALL-WIN32.md "readme files" are
now included in both the HTML and the PDF documentation.
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Store Erlang terms in 32-bit entities on the heap, expanding the
pointers to 64-bit when needed. This works because all terms are stored
on addresses in the 32-bit address range (the 32 most significant bits
of pointers to term data are always 0).
Introduce a new datatype called UWord (along with its companion SWord),
which is an integer having the exact same size as the machine word
(a void *), but might be larger than Eterm/Uint.
Store code as machine words, as the instructions are pointers to
executable code which might reside outside the 32-bit address range.
Continuation pointers are stored on the 32-bit stack and hence must
point to addresses in the low range, which means that loaded beam code
much be placed in the low 32-bit address range (but, as said earlier,
the instructions themselves are full words).
No Erlang term data can be stored on C stacks (enforced by an
earlier commit).
This version gives a prompt, but test cases still fail (and dump core).
The loader (and emulator loop) has instruction packing disabled.
The main issues has been in rewriting loader and actual virtual
machine. Subsystems (like distribution) does not work yet.
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The most important "readme" files now use Markdown notation. HTML
versions of these files are now also automatically generated and
included in the HTML documentation.
- Building and Installing Erlang/OTP - $ERL_TOP/INSTALL.md
(previously known as $ERL_TOP/README).
- Cross Compiling Erlang/OTP - $ERL_TOP/INSTALL-CROSS.md.
- How to Build Erlang/OTP on Windows - $ERL_TOP/INSTALL-WIN32.md
(previously known as $ERL_TOP/README.win32).
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improvements.
Most notable:
Lots of cross compilation improvements. The old cross compilation
support was more or less non-existing as well as broken. Please,
note that the cross compilation support should still be
considered as experimental. Also note that old cross compilation
configurations cannot be used without modifications. For more
information on cross compiling Erlang/OTP see the
$ERL_TOP/xcomp/README file.
Support for staged install using <url
href="http://www.gnu.org/prep/standards/html_node/DESTDIR.html">D
ESTDIR</url>. The old broken INSTALL_PREFIX has also been fixed.
For more information see the $ERL_TOP/README file.
Documentation of the release target of the top Makefile. For more
information see the $ERL_TOP/README file.
make install now by default creates relative symbolic links
instead of absolute ones. For more information see the
$ERL_TOP/README file.
$ERL_TOP/configure --help=recursive now works and prints help for
all applications with configure scripts.
Doing make install, or make release directly after make all no
longer triggers miscellaneous rebuilds.
Existing bootstrap system is now used when doing make install, or
make release without a preceding make all.
The crypto and ssl applications use the same runtime library path
when dynamically linking against libssl.so and libcrypto.so. The
runtime library search path has also been extended.
The configure scripts of erl_interface and odbc now search for
thread libraries and thread library quirks the same way as erts
do.
The configure script of the odbc application now also looks for
odbc libraries in lib64 and lib/64 directories when building on a
64-bit system.
The config.h.in file in the erl_interface application is now
automatically generated in instead of statically updated which
reduces the risk of configure tests without any effect.
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