llvm dev - Jan 2020 - LLVM build performance with LLVM

I have just tried a Release build of LLVM but
with
LIBOMPTARGET_ENABLE_DEBUG enabled. The app build became super fast, but I
can not obtain debugging information that I need at runtime.

On Sat, Jan 4, 2020 at 5:03 David Blaikie <dblaikie at gmail.com> wrote:
> I'm still confused by that - whether or not the LLVM you built has
debug
> info in it shouldn't at all change what goes into the binaries that
LLVM
> produces (modulo a few bugs, but nothing that'd produce drastic
performance
> swings). You mention in the bug that it's
> specifically LIBOMPTARGET_ENABLE_DEBUG that is slowing down your
> compilation time? Not the use of a Debug build of LLVM? Have you tried a
> Release build of LLVM but with LIBOMPTARGET_ENABLE_DEBUG enabled?
>
> On Fri, Jan 3, 2020 at 11:58 AM Itaru Kitayama <itaru.kitayama at
gmail.com>
> wrote:
>
>> At least, to obtain enough information from libomptarget while running
my
>> offloading app on GPU capable environment, I have to build it with an
LLVM
>> which was built in Debug mode.
>>
>> On Sat, Jan 4, 2020 at 4:34 David Blaikie <dblaikie at gmail.com>
wrote:
>>
>>>
>>>
>>> On Thu, Jan 2, 2020 at 10:55 PM Itaru Kitayama <itaru.kitayama
at gmail.com>
>>> wrote:
>>>
>>>> As I am facing the serious super slow down:
>>>> https://bugs.llvm.org/show_bug.cgi?id=44407 , I'd like to
>>>> learn more about how it can be minimized. When debugging an
app, there
>>>> are times building it with a
>>>> Debug build LLVM can not be avoided, but a situation like 40
times time
>>>> increase (40 minutes) is hard
>>>> to work with.
>>>>
>>>
>>> Not sure I follow - you shouldn't need a debug build of clang
to debug
>>> an application built with clang. You'd use a release build of
clang to
>>> build your application with debug info (by passing -g).
>>>
>>>
>>>>
>>>>
>>>> On Fri, Jan 3, 2020 at 11:14 AM David Blaikie <dblaikie at
gmail.com>
>>>> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Thu, Jan 2, 2020 at 6:09 PM Itaru Kitayama <
>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>
>>>>>> David,
>>>>>> Yes, I was indeed trying to build LLVM with a Debug
build. I'll stop
>>>>>> doing that from now on.
>>>>>>
>>>>>
>>>>> I mean, you can - it's just going to be super slow
& mostly not what
>>>>> you want, unless you're trying to debug that building
process. Usually
>>>>> you'd want to isolate one particular test case, maybe
even reduce it,
>>>>> before running it with a debug build of LLVM which will be
quite slow
>>>>> (because it's not optimized at all).
>>>>>
>>>>>
>>>>>> I am on JSC's JURON machine which has 251 GB of
memory on the login
>>>>>> node, that's more than sufficient
>>>>>> to do a build, I suppose, and the linker is LLD as LLVM
has a CMake
>>>>>> variable to select the linker.
>>>>>>
>>>>>
>>>>> Yep, sounds like you're just tripping over the fact
that an
>>>>> unoptimized/debug build of LLVM is very slow. *thumbs up*
>>>>>
>>>>>
>>>>>>
>>>>>> On Fri, Jan 3, 2020 at 11:02 AM David Blaikie
<dblaikie at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>> Were you trying to use a Debug build to build LLVM?
Yes, that would
>>>>>>> be very slow.
>>>>>>>
>>>>>>> If you mean you were using a release build of LLVM
to build a Debug
>>>>>>> build of LLVM - yeah, that's generally going to
be recommended. Did this
>>>>>>> get slower/change significantly in performance?
Many people have trouble
>>>>>>> with building Debug builds (no matter the host
compiler) especially if
>>>>>>> they're using bfd-ld, since it's quite
slow/uses a lot of memory. There are
>>>>>>> a few other issues to do with memory usage (do you
have less than about a
>>>>>>> GB of RAM per CPU? Then you'll probably hit
swapping by default & have a
>>>>>>> bad time - there are ways around that)
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Jan 2, 2020 at 5:42 PM Itaru Kitayama via
llvm-dev <
>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>
>>>>>>>> Hi,
>>>>>>>> When building LLVM, is it always recommended to
do it with the
>>>>>>>> latest official release, currently, it is
9.0.1? I ask because when
>>>>>>>> I tried
>>>>>>>> it with a Debug build, it took an enormous
amount of time on
>>>>>>>> POWER8.
>>>>>>>> _______________________________________________
>>>>>>>> LLVM Developers mailing list
>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>
>>>>>>>
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On Fri, Jan 3, 2020 at 5:58 PM Itaru Kitayama <itaru.kitayama at
gmail.com>
wrote:
> I have just tried a Release build of LLVM but
> with
> LIBOMPTARGET_ENABLE_DEBUG enabled. The app build became super fast, but I
> can not obtain debugging information that I need at runtime.
>
I know nothing about OMP, so I might be completely off-base with all of
this. But could you explain the specific steps you are taking (from
building the compiler, running the compiler to build your program,
executing the program, and what kind of debugging you are doing at
runtime/how you are doing it) including any commands you run to do those
actions, where possible?

>
> On Sat, Jan 4, 2020 at 5:03 David Blaikie <dblaikie at gmail.com>
wrote:
>
>> I'm still confused by that - whether or not the LLVM you built has
debug
>> info in it shouldn't at all change what goes into the binaries that
LLVM
>> produces (modulo a few bugs, but nothing that'd produce drastic
performance
>> swings). You mention in the bug that it's
>> specifically LIBOMPTARGET_ENABLE_DEBUG that is slowing down your
>> compilation time? Not the use of a Debug build of LLVM? Have you tried
a
>> Release build of LLVM but with LIBOMPTARGET_ENABLE_DEBUG enabled?
>>
>> On Fri, Jan 3, 2020 at 11:58 AM Itaru Kitayama <itaru.kitayama at
gmail.com>
>> wrote:
>>
>>> At least, to obtain enough information from libomptarget while
running
>>> my offloading app on GPU capable environment, I have to build it
with an
>>> LLVM which was built in Debug mode.
>>>
>>> On Sat, Jan 4, 2020 at 4:34 David Blaikie <dblaikie at
gmail.com> wrote:
>>>
>>>>
>>>>
>>>> On Thu, Jan 2, 2020 at 10:55 PM Itaru Kitayama <
>>>> itaru.kitayama at gmail.com> wrote:
>>>>
>>>>> As I am facing the serious super slow down:
>>>>> https://bugs.llvm.org/show_bug.cgi?id=44407 , I'd like
to
>>>>> learn more about how it can be minimized. When debugging an
app, there
>>>>> are times building it with a
>>>>> Debug build LLVM can not be avoided, but a situation like
40 times
>>>>> time increase (40 minutes) is hard
>>>>> to work with.
>>>>>
>>>>
>>>> Not sure I follow - you shouldn't need a debug build of
clang to debug
>>>> an application built with clang. You'd use a release build
of clang to
>>>> build your application with debug info (by passing -g).
>>>>
>>>>
>>>>>
>>>>>
>>>>> On Fri, Jan 3, 2020 at 11:14 AM David Blaikie <dblaikie
at gmail.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Thu, Jan 2, 2020 at 6:09 PM Itaru Kitayama <
>>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>>
>>>>>>> David,
>>>>>>> Yes, I was indeed trying to build LLVM with a Debug
build. I'll stop
>>>>>>> doing that from now on.
>>>>>>>
>>>>>>
>>>>>> I mean, you can - it's just going to be super slow
& mostly not what
>>>>>> you want, unless you're trying to debug that
building process. Usually
>>>>>> you'd want to isolate one particular test case,
maybe even reduce it,
>>>>>> before running it with a debug build of LLVM which will
be quite slow
>>>>>> (because it's not optimized at all).
>>>>>>
>>>>>>
>>>>>>> I am on JSC's JURON machine which has 251 GB of
memory on the login
>>>>>>> node, that's more than sufficient
>>>>>>> to do a build, I suppose, and the linker is LLD as
LLVM has a CMake
>>>>>>> variable to select the linker.
>>>>>>>
>>>>>>
>>>>>> Yep, sounds like you're just tripping over the fact
that an
>>>>>> unoptimized/debug build of LLVM is very slow. *thumbs
up*
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> On Fri, Jan 3, 2020 at 11:02 AM David Blaikie
<dblaikie at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Were you trying to use a Debug build to build
LLVM? Yes, that would
>>>>>>>> be very slow.
>>>>>>>>
>>>>>>>> If you mean you were using a release build of
LLVM to build a Debug
>>>>>>>> build of LLVM - yeah, that's generally
going to be recommended. Did this
>>>>>>>> get slower/change significantly in performance?
Many people have trouble
>>>>>>>> with building Debug builds (no matter the host
compiler) especially if
>>>>>>>> they're using bfd-ld, since it's quite
slow/uses a lot of memory. There are
>>>>>>>> a few other issues to do with memory usage (do
you have less than about a
>>>>>>>> GB of RAM per CPU? Then you'll probably hit
swapping by default & have a
>>>>>>>> bad time - there are ways around that)
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Jan 2, 2020 at 5:42 PM Itaru Kitayama
via llvm-dev <
>>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>> When building LLVM, is it always
recommended to do it with the
>>>>>>>>> latest official release, currently, it is
9.0.1? I ask because
>>>>>>>>> when I tried
>>>>>>>>> it with a Debug build, it took an enormous
amount of time on
>>>>>>>>> POWER8.
>>>>>>>>>
_______________________________________________
>>>>>>>>> LLVM Developers mailing list
>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>
>>>>>>>>
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On Fri, Jan 3, 2020 at 8:58 PM Itaru Kitayama via llvm-dev <
llvm-dev at lists.llvm.org> wrote:
> I have just tried a Release build of LLVM but
> with
> LIBOMPTARGET_ENABLE_DEBUG enabled. The app build became super fast, but I
> can not obtain debugging information that I need at runtime.
>
The description for this flag seems to be: LIBOMPTARGET_ENABLE_DEBUG "Allow
debug output with the environment variable LIBOMPTARGET_DEBUG=1"

Is this what you are looking for? Or are you looking into getting debug
info (Dwarf) for the OpenMP runtime itself?

-- 
Mehdi


>
> On Sat, Jan 4, 2020 at 5:03 David Blaikie <dblaikie at gmail.com>
wrote:
>
>> I'm still confused by that - whether or not the LLVM you built has
debug
>> info in it shouldn't at all change what goes into the binaries that
LLVM
>> produces (modulo a few bugs, but nothing that'd produce drastic
performance
>> swings). You mention in the bug that it's
>> specifically LIBOMPTARGET_ENABLE_DEBUG that is slowing down your
>> compilation time? Not the use of a Debug build of LLVM? Have you tried
a
>> Release build of LLVM but with LIBOMPTARGET_ENABLE_DEBUG enabled?
>>
>> On Fri, Jan 3, 2020 at 11:58 AM Itaru Kitayama <itaru.kitayama at
gmail.com>
>> wrote:
>>
>>> At least, to obtain enough information from libomptarget while
running
>>> my offloading app on GPU capable environment, I have to build it
with an
>>> LLVM which was built in Debug mode.
>>>
>>> On Sat, Jan 4, 2020 at 4:34 David Blaikie <dblaikie at
gmail.com> wrote:
>>>
>>>>
>>>>
>>>> On Thu, Jan 2, 2020 at 10:55 PM Itaru Kitayama <
>>>> itaru.kitayama at gmail.com> wrote:
>>>>
>>>>> As I am facing the serious super slow down:
>>>>> https://bugs.llvm.org/show_bug.cgi?id=44407 , I'd like
to
>>>>> learn more about how it can be minimized. When debugging an
app, there
>>>>> are times building it with a
>>>>> Debug build LLVM can not be avoided, but a situation like
40 times
>>>>> time increase (40 minutes) is hard
>>>>> to work with.
>>>>>
>>>>
>>>> Not sure I follow - you shouldn't need a debug build of
clang to debug
>>>> an application built with clang. You'd use a release build
of clang to
>>>> build your application with debug info (by passing -g).
>>>>
>>>>
>>>>>
>>>>>
>>>>> On Fri, Jan 3, 2020 at 11:14 AM David Blaikie <dblaikie
at gmail.com>
>>>>> wrote:
>>>>>
>>>>>>
>>>>>>
>>>>>> On Thu, Jan 2, 2020 at 6:09 PM Itaru Kitayama <
>>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>>
>>>>>>> David,
>>>>>>> Yes, I was indeed trying to build LLVM with a Debug
build. I'll stop
>>>>>>> doing that from now on.
>>>>>>>
>>>>>>
>>>>>> I mean, you can - it's just going to be super slow
& mostly not what
>>>>>> you want, unless you're trying to debug that
building process. Usually
>>>>>> you'd want to isolate one particular test case,
maybe even reduce it,
>>>>>> before running it with a debug build of LLVM which will
be quite slow
>>>>>> (because it's not optimized at all).
>>>>>>
>>>>>>
>>>>>>> I am on JSC's JURON machine which has 251 GB of
memory on the login
>>>>>>> node, that's more than sufficient
>>>>>>> to do a build, I suppose, and the linker is LLD as
LLVM has a CMake
>>>>>>> variable to select the linker.
>>>>>>>
>>>>>>
>>>>>> Yep, sounds like you're just tripping over the fact
that an
>>>>>> unoptimized/debug build of LLVM is very slow. *thumbs
up*
>>>>>>
>>>>>>
>>>>>>>
>>>>>>> On Fri, Jan 3, 2020 at 11:02 AM David Blaikie
<dblaikie at gmail.com>
>>>>>>> wrote:
>>>>>>>
>>>>>>>> Were you trying to use a Debug build to build
LLVM? Yes, that would
>>>>>>>> be very slow.
>>>>>>>>
>>>>>>>> If you mean you were using a release build of
LLVM to build a Debug
>>>>>>>> build of LLVM - yeah, that's generally
going to be recommended. Did this
>>>>>>>> get slower/change significantly in performance?
Many people have trouble
>>>>>>>> with building Debug builds (no matter the host
compiler) especially if
>>>>>>>> they're using bfd-ld, since it's quite
slow/uses a lot of memory. There are
>>>>>>>> a few other issues to do with memory usage (do
you have less than about a
>>>>>>>> GB of RAM per CPU? Then you'll probably hit
swapping by default & have a
>>>>>>>> bad time - there are ways around that)
>>>>>>>>
>>>>>>>>
>>>>>>>> On Thu, Jan 2, 2020 at 5:42 PM Itaru Kitayama
via llvm-dev <
>>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>>
>>>>>>>>> Hi,
>>>>>>>>> When building LLVM, is it always
recommended to do it with the
>>>>>>>>> latest official release, currently, it is
9.0.1? I ask because
>>>>>>>>> when I tried
>>>>>>>>> it with a Debug build, it took an enormous
amount of time on
>>>>>>>>> POWER8.
>>>>>>>>>
_______________________________________________
>>>>>>>>> LLVM Developers mailing list
>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>
>>>>>>>> _______________________________________________
> LLVM Developers mailing list
> llvm-dev at lists.llvm.org
> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>
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Yes, exactly.

On Sun, Jan 5, 2020 at 23:43 Mehdi AMINI <joker.eph at gmail.com> wrote:
>
>
> On Fri, Jan 3, 2020 at 8:58 PM Itaru Kitayama via llvm-dev <
> llvm-dev at lists.llvm.org> wrote:
>
>> I have just tried a Release build of LLVM but
>> with
>> LIBOMPTARGET_ENABLE_DEBUG enabled. The app build became super fast, but
I
>> can not obtain debugging information that I need at runtime.
>>
>
> The description for this flag seems to be: LIBOMPTARGET_ENABLE_DEBUG
> "Allow debug output with the environment variable
LIBOMPTARGET_DEBUG=1"
>
> Is this what you are looking for? Or are you looking into getting debug
> info (Dwarf) for the OpenMP runtime itself?
>
> --
> Mehdi
>
>
>
>>
>> On Sat, Jan 4, 2020 at 5:03 David Blaikie <dblaikie at gmail.com>
wrote:
>>
>>> I'm still confused by that - whether or not the LLVM you built
has debug
>>> info in it shouldn't at all change what goes into the binaries
that LLVM
>>> produces (modulo a few bugs, but nothing that'd produce drastic
performance
>>> swings). You mention in the bug that it's
>>> specifically LIBOMPTARGET_ENABLE_DEBUG that is slowing down your
>>> compilation time? Not the use of a Debug build of LLVM? Have you
tried a
>>> Release build of LLVM but with LIBOMPTARGET_ENABLE_DEBUG enabled?
>>>
>>> On Fri, Jan 3, 2020 at 11:58 AM Itaru Kitayama <itaru.kitayama
at gmail.com>
>>> wrote:
>>>
>>>> At least, to obtain enough information from libomptarget while
running
>>>> my offloading app on GPU capable environment, I have to build
it with an
>>>> LLVM which was built in Debug mode.
>>>>
>>>> On Sat, Jan 4, 2020 at 4:34 David Blaikie <dblaikie at
gmail.com> wrote:
>>>>
>>>>>
>>>>>
>>>>> On Thu, Jan 2, 2020 at 10:55 PM Itaru Kitayama <
>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>
>>>>>> As I am facing the serious super slow down:
>>>>>> https://bugs.llvm.org/show_bug.cgi?id=44407 , I'd
like to
>>>>>> learn more about how it can be minimized. When
debugging an app,
>>>>>> there are times building it with a
>>>>>> Debug build LLVM can not be avoided, but a situation
like 40 times
>>>>>> time increase (40 minutes) is hard
>>>>>> to work with.
>>>>>>
>>>>>
>>>>> Not sure I follow - you shouldn't need a debug build of
clang to debug
>>>>> an application built with clang. You'd use a release
build of clang to
>>>>> build your application with debug info (by passing -g).
>>>>>
>>>>>
>>>>>>
>>>>>>
>>>>>> On Fri, Jan 3, 2020 at 11:14 AM David Blaikie
<dblaikie at gmail.com>
>>>>>> wrote:
>>>>>>
>>>>>>>
>>>>>>>
>>>>>>> On Thu, Jan 2, 2020 at 6:09 PM Itaru Kitayama <
>>>>>>> itaru.kitayama at gmail.com> wrote:
>>>>>>>
>>>>>>>> David,
>>>>>>>> Yes, I was indeed trying to build LLVM with a
Debug build. I'll
>>>>>>>> stop doing that from now on.
>>>>>>>>
>>>>>>>
>>>>>>> I mean, you can - it's just going to be super
slow & mostly not what
>>>>>>> you want, unless you're trying to debug that
building process. Usually
>>>>>>> you'd want to isolate one particular test case,
maybe even reduce it,
>>>>>>> before running it with a debug build of LLVM which
will be quite slow
>>>>>>> (because it's not optimized at all).
>>>>>>>
>>>>>>>
>>>>>>>> I am on JSC's JURON machine which has 251
GB of memory on the login
>>>>>>>> node, that's more than sufficient
>>>>>>>> to do a build, I suppose, and the linker is LLD
as LLVM has a CMake
>>>>>>>> variable to select the linker.
>>>>>>>>
>>>>>>>
>>>>>>> Yep, sounds like you're just tripping over the
fact that an
>>>>>>> unoptimized/debug build of LLVM is very slow.
*thumbs up*
>>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>> On Fri, Jan 3, 2020 at 11:02 AM David Blaikie
<dblaikie at gmail.com>
>>>>>>>> wrote:
>>>>>>>>
>>>>>>>>> Were you trying to use a Debug build to
build LLVM? Yes, that
>>>>>>>>> would be very slow.
>>>>>>>>>
>>>>>>>>> If you mean you were using a release build
of LLVM to build a
>>>>>>>>> Debug build of LLVM - yeah, that's
generally going to be recommended. Did
>>>>>>>>> this get slower/change significantly in
performance? Many people have
>>>>>>>>> trouble with building Debug builds (no
matter the host compiler) especially
>>>>>>>>> if they're using bfd-ld, since it's
quite slow/uses a lot of memory. There
>>>>>>>>> are a few other issues to do with memory
usage (do you have less than about
>>>>>>>>> a GB of RAM per CPU? Then you'll
probably hit swapping by default & have a
>>>>>>>>> bad time - there are ways around that)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On Thu, Jan 2, 2020 at 5:42 PM Itaru
Kitayama via llvm-dev <
>>>>>>>>> llvm-dev at lists.llvm.org> wrote:
>>>>>>>>>
>>>>>>>>>> Hi,
>>>>>>>>>> When building LLVM, is it always
recommended to do it with the
>>>>>>>>>> latest official release, currently, it
is 9.0.1? I ask because
>>>>>>>>>> when I tried
>>>>>>>>>> it with a Debug build, it took an
enormous amount of time on
>>>>>>>>>> POWER8.
>>>>>>>>>>
_______________________________________________
>>>>>>>>>> LLVM Developers mailing list
>>>>>>>>>> llvm-dev at lists.llvm.org
>>>>>>>>>>
https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>>>>>>>>>
>>>>>>>>>
_______________________________________________
>> LLVM Developers mailing list
>> llvm-dev at lists.llvm.org
>> https://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-dev
>>
>
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