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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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* raimo/close-ports-on-halt/OTP-9985:
erts: Basic test of erlang:halt/0..2
erts: Document erlang:halt/2 and update erlang:halt/0,1
erts: Implement erlang:halt/2
stdlib: Stop working around erlang:halt not flushing
erts: Make erlang:halt/0,1 close ports and flush async threads
erts: Remove forgotten and unused function erl_exit0
erts: Implement erl_halt
erts: Remove unused ntbuild.erl
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* sverk/cpu-topology-crash:
erts: Fix memory corruption when reading topology info
OTP-10004
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* dc/dch-fix-win32-escript:
add escript win32 alternative invocation (thanks Pierre Rouleau)
OTP-9997
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* sverk/zlib_port_leak:
Fix port leaks in zlib
OTP-9981
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* ps/inet6-less-build-fix:
Add missing HAVE_IN6 && AF_INET6 ifdef
OTP-9996
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* lukas/kernel/sendfile_fixes:
Fix reselecting bug on OS X
Fix bug when sending long files using select
Fix ifdef to check if we are on OS X
Add test case for sending multiple small files on same connection
Fix memory leak when sendfile process crashes
Extend timeout for windows
Skip sendfile suite if solaris 8
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Since stop_select is called at an arbitrary point in the future
it would sometime not be alled before the tcp driver started
selecting on the fd. So now ERL_DRV_USE_NO_CALLBACK is used
so that the stop_select call is never made.
This seems to only have happened OS X.
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The return value from efile_sendfile was not consistent
inbetween platforms. The API should now be working as it
was intended.
OTP-9994
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We use the fact that file_flush is called when there is
data in the driver queue when a port is closed to ensure
that all data is cleaned up as it should.
OTP-9993
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* bjorn/kernel/erts_debug_size-fix/OTP-9991:
Improve erts_debug_SUITE
Fix calculation of fun size in erts_debug:size/1
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Test erts_debug:size/1 too. Also test funs and shared terms.
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* ph/fix-enfile/OTP-9990:
Update preloaded prim_inet.beam
gen_tcp: Use correct specs for accept and listen
prim_inet: Catch system_limit in open_port
Fix returned error from gen_tcp:accept/1,2 when running out of ports
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Will catch system_limit and return error tuple instead. An uncaught
exception would be an incorrect behaviour. This problem would occur
for gen_tcp:listen/1,2 for example.
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If the number of processors actually found while reading sysfs
is lower than the configured value, we realloc() the cpuinfo array
to the smaller size, but we then iterate it using the original
configured size, thus corrupting memory beyond the allocated
block.
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zip,unzip,gzip,gunzip,compress and uncompress did not close the port
when given invalid data argument. Fixed by putting close in "try-after".
A closed port could in same cases get stuck in limbo due to data in
io-queue. Fixed by adding a flush callback.
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* rickard/barriers/OTP-9922:
Remove newly introduced excessive barrier in erts_thr_progress_later()
Fix implementation with ddrb barriers
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* sverk/cpu-topology-crash:
erts: Fix crash on Linux if /sys/devices/system/node is not readable
OTP-9978
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* egil/redocument-scheduler_wall_time/OTP-9858:
doc: Enhance wording and remove typos
doc: Move examples and notes into tag-lists
doc: Rewording of scheduler_wall_time
doc: Change variable name to 'A' to reflect Active
doc: Rewording of scheduler busy
Update scheduler_wall_time documentation
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* lukas/system/ssh_undef_function:
Add filter for ssh undefined function calls
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Fallback on using /sys/devices/system/cpu to get cpu topology,
as is already done when node directory doesn't exist.
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* Add example on calculating scheduler utilization
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* rickard/barriers/OTP-9922:
Fix implementation with ddrb barriers
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This prevents building for operating systems that do not yet have IPv6
compatible socket API. Error can be reproduced by (cross)building for
a os that doesn't have these headers. This will abort with a error
about incomplete type 'struct in6_addr'. All other uses of IPv6 API
in inet_drv.c are conditionalized like in the patch.
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A large 64-bit immediate number will be stored as SMALL_BIG_EXT by ETS
compressed format. When uncompressing, the SMALL_BIG_EXT was first
decoded as as bignum (by bytes_to_big) and then turned into a small
(by big_norm). This works for normal "binary_to_term" as
decoded_size() over-estimates the needed heap size. But for ETS no
over-estimation is done as the real term size is known and stored in
DbTerm.
Fixed by preventing bytes_to_big() from writing bignum digit when the
number is seen to fit in an immediate.
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* rickard/barriers/OTP-9922:
Reduce thread progress read operations in handle_aux_work()
Misc memory barrier fixes
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- Document barrier semantics
- Introduce ddrb suffix on atomic ops
- Barrier macros for both non-SMP and SMP case
- Make the thread progress API a bit more intuitive
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* jz/erts-remove-unused-var:
erts: Remove unused variable
OTP-9926
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* rc/spell-registered:
Correct spelling of "registered" in various places in the source code
OTP-9925
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