[argobots-discuss] Argobots ABT_eventual_set too slow

[Iwasaki, Shintaro]

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<mailto: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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