[argobots-discuss] Argobots ABT_eventual_set too slow

[Houjun Tang]

Hi Shintaro,

Thanks for the quick reply, here is a brief summary of what I have been
working on.
I'm adding the asynchronous I/O feature to the HDF5 library using Argobots
as the background thread execution engine. So whenever there is an HDF5 I/O
call, the main thread will create an Argobots task (with ABT_task_create)
and have it executed by Argobots in the background. Only one Argobots pool
is used, so consecutive tasks are executed sequentially. The application
code linked to the async HDF5 library is creating and writing a lot of HDF5
attributes, as seen in the figure I sent previously, the time taken by
ABT_eventual_set varies greatly, from 2 us to 0.45 s with an average ~0.07s.

Any additional information would you like to know? Do you want the code?


Regards,
Houjun Tang

On Fri, Apr 19, 2019 at 2:11 PM Iwasaki, Shintaro via discuss <
discuss at lists.argobots.org> wrote:

> Hello Houjun,
>
> Thank you for reporting a performance issue with data!
> Unfortunately, I haven't experienced this issue. I checked the code, but
> it is hard to judge if the implementation of ABT_eventual_set is bad or
> not. As far as I checked the implementation of ABT_eventual_set, this
> function does not looks very optimized (I mean, it uses a naive spinlock),
> but doe not seem very slow (I mean, it does not allocate memory every time).
> https://github.com/pmodels/argobots/blob/master/src/eventual.c#L229
>
> In any case, this single operation should be finished within 1us or less
> (under no contention). I guess it might be caused by a scheduling issue or
> an affinity issue, but since the performance of this function has not been
> fully examined, the current implementation might have some performance
> bugs. I could diagnose this problem more if you would give me more details.
>
> Thank You,
> Shintaro Iwasaki
>
> On Fri, Apr 19, 2019 at 2:56 PM Houjun Tang via discuss <
> discuss at lists.argobots.org> wrote:
>
>> Hi,
>>
>> I'm using Argobots as the engine for executing asynchronous I/O
>> operations in the background of an HDF5 application, but found it to be
>> slow in some operations. With profiling, the slowdown comes mostly from
>> *ABT_eventual_set*. Below is a boxplot of the ABT_eventual_set time
>> (measured by calling gettimeofday before and after it) from 385 operations,
>> running with one process and one Argobots thread. The *_fn are different
>> functions executed by Argobots. In most cases it's below 0.1s, but there
>> are several cases that are taking more than 0.25 seconds. As these HDF5
>> operations take less than 0.1 seconds, the overhead of ABT_eventual_set
>> becomes dominant.
>>
>> Any idea what could have caused this?
>>
>> Thanks,
>> Houjun Tang
>>
>>
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>>
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