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From Pedro Larroy <pedro.larroy.li...@gmail.com>
Subject Re: Please remove conflicting Open MP version from CMake builds
Date Mon, 09 Dec 2019 00:42:30 GMT
Great investigation thank you. I have to agree with your analysis and for
helping resolving this long standing issue.

This will not repair the damage made to the community of losing 3-4
valuable contributors. Introducing a library that causes bugs then blocking
changes and locking gh issues which attempt to remove or workaround the
issues in addition to making rude comments and worse things that are better
left out is still not acceptable and begs for an apology from Chris.

P.




On Sunday, December 8, 2019, Lausen, Leonard <lausen@amazon.com.invalid>
wrote:
> Thanks Pedro and Chris for your responses.
>
> After further investigation I find:
>
> 1) I don't think https://github.com/apache/incubator-mxnet/issues/14979 is
> caused by any incompatibility between gomp and llvm / intel omp. Rather
it's
> simply a problem of llvm / intel omp. See my comment to the issue for the
> methodology to arrive at this claim.
>
> 2) Regarding the assertion failure when compiling with (llvm)
3rdparty/openmp,
> it can be fixed by updating the by now 2 years old llvm openmp code to the
> newest released version. I went ahead and opened a PR
> https://github.com/apache/incubator-mxnet/pull/17012
>
> Based on the investigation described in 1), I think Chris is right that
the
> assertion failure is not due to some interaction between gomp and llvm
omp.
> However, I'm not sure about Chris's suggestion that the assertion failure
is due
> to a bug in MXNet. In fact, the failure goes away when updating the llvm
openmp
> code. So I think it's just due to a bug in the 2 years old code.
>
> @Chris, I think updating 3rdparty/openmp to fix the assertion issue is not
> contentious. Thus let's do it via lazy consensus (72 hours) or just
approve the
> PR and merge it.
>
> Please also take a look at my comment at #14979 and let everyone know if
you see
> any option to fix the bug while keeping 3rdparty/openmp. As this bug
affects an
> important use-case, I beleive we need to remove 3rdparty/openmp from the
CMake
> build as long as we don't find a solution for making #14979 work with
> 3rdparty/openmp.
>
> In fact, removing 3rdparty/openmp will then match the current Makefile
setup
> that according to my understanding is used to build the nightly releases
used by
> the majority of developers. Ie. most users actually don't use the CMake
build
> with 3rdparty/openmp. You can consider rescinding your veto on removing
> 3rdparty/openmp after reading through the evidence in that issue. If you
don't
> provide any evidence for why the methodology/conclusion in #14979 is
flawed, I
> will assume your previous veto is void based on Apache Voting rule as it
lacks
> technical justification and in any case was motivated by the assertion
issue,
> which I agree with you, is likely not due to gomp / omp interaction.
>
> Thank you
> Leonard
>
>
> On Sat, 2019-12-07 at 15:40 -0800, Pedro Larroy wrote:
>> Stop disseminating false information:
>>
>> https://github.com/apache/incubator-mxnet/issues/14979
>>
>>
>> On Sat, Dec 7, 2019 at 7:04 AM Chris Olivier <cjolivier01@gmail.com>
wrote:
>>
>> > -1
>> >
>> > mkldnn removed omp5 for licencing issues
>> > no bugs have actually been traced to the use of llvm openmp. only an
assert
>> > caused by an actual bug in mxnet code. there are suitable workarounds.
>> >
>> > over time llvm omp has simply been used as a “catch all” for random
>> > problems that aren’t related at all (such as getenv race condition in
an
>> > atfork call that isn’t even part of an omp parallel region).
>> >
>> > proposal is now and has always been roughly equivalent to the idea of
>> > “comment out an assert rather than fix the bug it’s reporting”.
>> >
>> > Up until very recently, Makefile version of mxnet used libomp5 for
YEARS
>> > and not libgomp, with no issue reported (omp not built in debug mode),
so
>> > the equivalent configuration from CMake mysteriously causing myriads if
>> > problems has questionable merit and smells more like a hubris
situation.
>> >
>> > I use tensorflow as well and it links to libomp5 rather than libgomp.
>> >
>> > if the assert problem is really a problem, the bug being reported
would be
>> > prioritized and fixed. it should be fixed regardless. all the time
spent by
>> > some CI people trying to remove this could have simply fixed the
actual bug
>> > in a small fraction of the time.
>> >
>> >
>> > On Fri, Dec 6, 2019 at 8:44 PM Lausen, Leonard
<lausen@amazon.com.invalid>
>> > wrote:
>> >
>> > > I think it's reasonable to assume that the Intel MKLDNN team is an
>> > > "authorative"
>> > > source about the issue of compilation with OpenMP and the OpenMP
runtime
>> > > library
>> > > related issues. Thus I suggest we follow the recommendation of Intel
>> > > MKLDNN team
>> > > within the MXNet project.
>> > >
>> > > Looking through the Intel MKLDNN documentation, I find [1]:
>> > >
>> > > > DNNL uses OpenMP runtime library provided by the compiler.
>> > >
>> > > as well as
>> > >
>> > > > it's important to ensure that only one OpenMP runtime is used
>> > throughout
>> > > the
>> > > > application. Having more than one OpenMP runtime linked to an
>> > executable
>> > > may
>> > > > lead to undefined behavior including incorrect results or crashes.
>> > >
>> > > To keep our project maintainable and error free, I thus suggest we
follow
>> > > DNNL
>> > > and use the OpenMP runtime library provided by the compiler.
>> > > We have limited ressources and finding the root cause for any bugs
>> > > resulting
>> > > from linking multiple OpenMP libraries as currently done is, in my
>> > > opinion. not
>> > > a good use of time. We know it's due to undefined behavior and we
know
>> > > it's best
>> > > practice to use OpenMP runtime library provided by the compiler. So
let's
>> > > just
>> > > do that.
>> > >
>> > > I think given that MKL-DNN has also adopted the "OpenMP runtime
library
>> > > provided
>> > > by the compiler" approach, this issue is not contentious anymore and
>> > > qualifies
>> > > for lazy consensus.
>> > >
>> > > Thus if there is no objection within 72 hours (lazy consensus), let's
>> > drop
>> > > bundled LLVM OpenMP from master [2]. If we find any issues due to
>> > > droppeing the
>> > > bundled LLVM OpenMP, we can always add it back prior to the next
release.
>> > >
>> > > Best regards
>> > > Leonard
>> > >
>> > > [1]:
>> > >
>> > >
>> >
https://github.com/intel/mkl-dnn/blob/433e086bf5d9e5ccfc9ec0b70322f931b6b1921d/doc/build/build_options.md#openmp
>> > > (This is the updated reference from Anton's previous comment, based
on
>> > the
>> > > changes in MKLDNN done in the meantime
>> > >
>> >
https://github.com/apache/incubator-mxnet/pull/12160#issuecomment-415078066
>> > > )
>> > > [2]: Alike https://github.com/apache/incubator-mxnet/pull/12160
>> > >
>> > >
>> > > On Fri, 2019-12-06 at 12:16 -0800, Pedro Larroy wrote:
>> > > > I will try to stay on the sidelines for now since previous
>> > conversations
>> > > > about OMP have not been productive here and I have spent way too
much
>> > > time
>> > > > on this already, I'm not the first one giving up on trying to help
with
>> > > > this topic.
>> > > >
>> > > > I would be glad if you guys can work together and find a solution.
I
>> > will
>> > > > just put my understanding of the big picture hoping that it helps
move
>> > it
>> > > > forward.
>> > > >
>> > > >
>> > > > Recently the intel omp library which seemed to have the best
>> > performance
>> > > of
>> > > > the 3 was removed from MKL.
>> > > >
>> > > > - There's 3 libraries in play, GNU Omp which is shipped with gcc
>> > (gomp),
>> > > > LLVM openmp in 3rdparty (llvm-omp), Intel OMP when using MKL,
which is
>> > > > recently removed (iomp)
>> > > >
>> > > > - IOMP seems to have the best performance, there's stability issues
>> > > > producing crashes sometimes but the impact seems relatively small
for
>> > > users
>> > > > and developers. In general seems linking with a different OMP
version
>> > > that
>> > > > the one shipped with the compiler is known to cause stability
issues
>> > but
>> > > > it's done anyway.
>> > > >
>> > > > - LLVM-OMP used when building with CMake, not used in the PIP
releases
>> > or
>> > > > when building with Make. Has stability issues, hangs when running
in
>> > > debug
>> > > > mode during test execution and produces tons of assertions in debug
>> > mode.
>> > > > Might have some small performance gains but there is no clear cut
data
>> > > that
>> > > > showcases significant performance gains.
>> > > >
>> > > > - GOMP is the version shipped with GCC and the PIP wheels without
MKL,
>> > > has
>> > > > no stability problems.
>> > > >
>> > > > As a ballpark, IOMP might give 10% performance improvement in some
>> > cases.
>> > > > We need to document well how users should tune and configure MXNet
when
>> > > > using OMP.
>> > > >
>> > > > As a developer, the safest bet is to use GOMP to be able to debug
and
>> > > > develop without issues. As a user of CPU inference / training you
want
>> > to
>> > > > run MKL so depends on how the Intel guys want to do things. My
>> > preference
>> > > > as an engineer is always stability > speed.
>> > > >
>> > > > Related tickets:
>> > > >
>> > > > https://github.com/apache/incubator-mxnet/issues/16891
>> > > >
>> > > >
>> >
https://github.com/apache/incubator-mxnet/issues/10856#issuecomment-562637931
>> > > >
>> > > > https://github.com/apache/incubator-mxnet/issues/11417
>> > > >
>> > > > https://github.com/apache/incubator-mxnet/issues/15690
>> > > >
>> > > >
>> > > >
>> > > > On Fri, Dec 6, 2019 at 12:39 AM Lausen, Leonard
>> > > <lausen@amazon.com.invalid>
>> > > > wrote:
>> > > >
>> > > > > Is this related to
>> > > https://github.com/apache/incubator-mxnet/issues/10856?
>> > > > > I unlocked that Github issue based on the Apache Code of Conduct
>> > > > >
>> > https://www.apache.org/foundation/policies/conduct#specific-guidelines
>> > > > >
>> > > > > On Sat, 2019-11-30 at 02:47 -0800, Pedro Larroy wrote:
>> > > > > > (py3_venv) piotr@34-215-197-42:1:~/mxnet_1.6
(upstream_master)+$
>> > ldd
>> > > > > > build/libmxnet.so| grep -i openmp
>> > > > > >         libomp.so =>
>> > > > > >
/home/piotr/mxnet_1.6/build/3rdparty/openmp/runtime/src/libomp.so
>> > > > > > (0x00007fde0991d000)
>> > > > > > (py3_venv) piotr@34-215-197-42:0:~/mxnet_1.6
(upstream_master)+$
>> > > python
>> > > > > > ~/deeplearning-benchmark/image_classification/infer_imagenet.py
>> > > --use-rec
>> > > > > > --batch-size 256 --dtype float32 --num-data-workers 40 --mode
>> > hybrid
>> > > > > > --model resnet50_v2 --use-pretrained --kvstore local
>> > --log-interval 1
>> > > > > > --rec-val ~/data/val-passthrough.rec --rec-val-idx
>> > > > > > ~/data/val-passthrough.idx
>> > > > > > INFO:root:Namespace(batch_norm=False, batch_size=256,
>> > > > > > data_dir='~/.mxnet/datasets/imagenet', dataset_size=32,
>> > > dtype='float32',
>> > > > > > kvstore='local', last_gamma=False, log_interval=1,
>> > > logging_dir='logs',
>> > > > > > lr=0.1, lr_decay=0.1, lr_decay_epoch='40,60', lr_mode='step',
>> > > > > > lr_poly_power=2, mode='hybrid', model='resnet50_v2',
momentum=0.9,
>> > > > > > num_epochs=3, num_gpus=0, num_workers=40,
>> > > > > > rec_val='/home/piotr/data/val-passthrough.rec',
>> > > > > > rec_val_idx='/home/piotr/data/val-passthrough.idx',
>> > > save_dir='params',
>> > > > > > save_frequency=0, top_k=0, use_pretrained=True, use_rec=True,
>> > > > > use_se=False,
>> > > > > > warmup_epochs=0, warmup_lr=0.0, wd=0.0001)
>> > > > > > [10:42:02] ../src/io/iter_image_recordio_2.cc:178:
>> > > ImageRecordIOParser2:
>> > > > > > /home/piotr/data/val-passthrough.rec, use 36 threads for
decoding..
>> > > > > > INFO:root:Batch [0]
>> > > > > > INFO:root:Top 1 accuracy: 0
>> > > > > > INFO:root:warmup_throughput: 5 samples/sec warmup_time
43.150922
>> > > > > > INFO:root:Batch [1]
>> > > > > > INFO:root:Top 1 accuracy: 0
>> > > > > > INFO:root:warmup_throughput: 6 samples/sec warmup_time
37.971927
>> > > > > > INFO:root:Batch [2]
>> > > > > > INFO:root:Top 1 accuracy: 0
>> > > > > > INFO:root:warmup_throughput: 7 samples/sec warmup_time
35.755363
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > >
>> > > > > > (py3_venv) piotr@34-215-197-42:0:~/mxnet_1.6_plat_omp
>> > > > > (upstream_master)+$
>> > > > > > git st
>> > > > > > On branch upstream_master
>> > > > > > Your branch is up to date with 'origin/upstream_master'.
>> > > > > >
>> > > > > > Changes not staged for commit:
>> > > > > >   (use "git add/rm <file>..." to update what will
be committed)
>> > > > > >   (use "git checkout -- <file>..." to discard changes
in
working
>> > > > > directory)
>> > > > > >         deleted:    3rdparty/openmp
>> > > > > >
>> > > > > > no changes added to commit (use "git add" and/or "git commit
-a")
>> > > > > > (py3_venv) piotr@34-215-197-42:1:~/mxnet_1.6_plat_omp
>> > > > > (upstream_master)+$
>> > > > > > ldd build/libmxnet.so | grep -i omp
>> > > > > >         libgomp.so.1 => /usr/lib/x86_64-linux-gnu/libgomp.so.1
>> > > > > > (0x00007f941241c000)
>> > > > > >
>> > > > > > (py3_venv) piotr@34-215-197-42:130:~/mxnet_1.6_plat_omp
>> > > > > (upstream_master)+$
>> > > > > > python
>> > > ~/deeplearning-benchmark/image_classification/infer_imagenet.py
>> > > > > > --use-rec --batch-size 256 --dtype float32 --num-data-workers
40
>> > > --mode
>> > > > > > hybrid --model resnet50_v2 --use-pretrained --kvstore local
>> > > > > --log-interval
>> > > > > > 1 --rec-val ~/data/val-passthrough.rec --rec-val-idx
>> > > > > > ~/data/val-passthrough.idx
>> > > > > > INFO:root:warmup_throughput: 147 samples/sec warmup_time
1.735117
>> > > > > > INFO:root:Batch [16]
>> > > > > > INFO:root:Top 1 accuracy: 0
>> > > > > > INFO:root:warmup_throughput: 143 samples/sec warmup_time
1.785760
>> > > > > > INFO:root:Batch [17]
>> > > > > > INFO:root:Top 1 accuracy: 0
>> > > > > > INFO:root:warmup_throughput: 148 samples/sec warmup_time
1.729033
>

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