[LLVMdev] [lldb-dev] RFC: LLVM should require a working C++11 <thread>, <mutex>, and <atomic>

[Yaron Keren]

Hi Vadim,

Yes, exactly, what is the point of having two versions -pthreads and
-win32threads when you can make -pthreads behave like -win32threads by
disabling the use of pthreads etc?

Yaron


2014-09-26 22:47 GMT+03:00 Vadim Chugunov <vadimcn at gmail.com>:

> When LLVM's configure finds a usable <pthread.h>, it prefers to use that
> rather than the home-grown stuff.   However if LLVM is configured with
> --disable-pthreads, both mingw flavors produce the same results.
>
> BTW, I've tried to quantify the slowdown: a quick test indicates that LLVM
> build that uses pthreads is about 10% slower than the one which doesn't.
> This is less that I remember seeing last year (something got optimized?),
> but still...
>
> Vadim
>
>
> On Fri, Sep 26, 2014 at 3:29 AM, Yaron Keren <yaron.keren at gmail.com>
> wrote:
>
>> Yes, of course.
>>
>> I refer to the  significant slowdown of Rust compiler when compiled with
>> -pthreads vs -win32threads flavor.
>> If Rust can be compiled without <mutex> and <thread> on win32threads, why
>> should it slow down on pthreads?
>> Isn't the only difference betwen the win32threads and pthreads is the
>> addition of pthreads, <mutex> and <thread>?
>>
>> Yaron
>>
>>
>> 2014-09-26 11:39 GMT+03:00 Vadim Chugunov <vadimcn at gmail.com>:
>>
>>> Hi Yaron,
>>> Not sure I understand your question.  Wasn't <mutex> one of the more
>>> important C++11 features that LLVM would like to use?
>>>
>>
>> On Thu, Sep 25, 2014 at 1:24 AM, Yaron Keren <yaron.keren at gmail.com>
>> wrote:
>>
>>> Vadim,
>>>
>>> Thanks for the feedback on the -win32. A dependency on a small DLL with
>>> BSD license does not sound too bad, but performance regression is obviously
>>> a serious problem.
>>>
>>> However, by disabling <mutex> use with -pthreads rust performance should
>>> be same as -win32 threads?
>>> Saying it another way, does the -win32 version have any feature that
>>> -pthreads vesion do not have?
>>>
>>> Yaron
>>>
>>>
>>> 2014-09-25 9:52 GMT+03:00 Vadim Chugunov <vadimcn at gmail.com>:
>>>
>>>> Hi,
>>>> I think I can at least answer why the Rust project prefers to use
>>>> mingw-w64-win32threads:
>>>> 1. It does not inject dependency on libwinpthread.dll, which is nice.
>>>> 2. Those who tried building LLVM with mingw-w64-pthreads, had reported
>>>> significant slowdown of the resulting Rust compiler (as compared to one
>>>> linked to LLVM compiled with the win32threads flavor).   Profiling seemed
>>>> to point towards libpthreads' implementation of mutex.  I had checked the
>>>> source, and indeed, it looked not very efficient (
>>>> http://sourceforge.net/p/mingw-w64/bugs/344).  It would be nice to get
>>>> a second opinion, though, maybe I missed something.
>>>>
>>>> Vadim
>>>>
>>>>
>>>> On Wed, Sep 24, 2014 at 10:55 AM, Chandler Carruth <
>>>> chandlerc at google.com> wrote:
>>>>
>>>>>
>>>>> On Wed, Sep 24, 2014 at 10:37 AM, Óscar Fuentes <ofv at wanadoo.es>
>>>>> wrote:
>>>>>
>>>>>> The best thing for understanding their reasons is to ask them to speak
>>>>>> up.
>>>>>>
>>>>>
>>>>> I asked them directly, and this thread is a chance for them to speak
>>>>> up again. I *think* I've addressed the concerns of those I've spoken to
>>>>> directly, but there may be other folks or other concerns or I may have
>>>>> messed it up. =]
>>>>>
>>>>>
>>>>>> My experience on the MinGW/MinGW-w64 communities is that those who
>>>>>> choose MinGW is because of ignorance about MinGW-w64 and because there
>>>>>> are lots of documents on the 'net that references MinGW. MinGW is, to
>>>>>> all practical effects, a zombie project and there is no reason to
>>>>>> prefer
>>>>>> it over MinGW-w64 nowadays.
>>>>>>
>>>>>
>>>>> :: shrug ::
>>>>>
>>>>> I'm not such a user, and so I don't want to speculate as to what
>>>>> motivates them.
>>>>>
>>>>> _______________________________________________
>>>>> LLVM Developers mailing list
>>>>> LLVMdev at cs.uiuc.edu         http://llvm.cs.uiuc.edu
>>>>> http://lists.cs.uiuc.edu/mailman/listinfo/llvmdev
>>>>>
>>>>>
>>>>
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>>>>
>>>>
>>>
>>
>
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