[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

Unfortunately they will not be backported, that's against our release policies, 
and I can't do anything about it.  You can backport them yourself and build 
your own CPython 3.6.  That's what bigger users (e.g. Facebook/Google) of 
Python usually do.

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

Yuri, Those speed improvements are awesome and I'm really excited about them, 
performance is slowly starting to match asynq and would make us migrating our 
code to async/await more feasable!

Today, python3.6.4 was released and these performance improvements did not make 
it in this version.

I'm not familiar with python's release processes , what are the steps or time 
line for these to be backported to 3.6 and released on next minor version as to 
avoid a lengthy wait for python3.7?

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[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

NP.  I have another PR in the pipeline: 
https://github.com/python/cpython/pull/4913

Both optimizations make your benchmark run 30% faster on 3.7.  If you compile 
asyncio.gather() with Cython you will get it another 5-15% faster.  If you use 
uvloop - another 10-20%.

If it's still slower than asynq, then the issue must be in how asynq schedules 
its callbacks, it might be more optimal for some specific use cases than 
asyncio.

FWIW I don't expect asynq to be any faster than asyncio (or than uvloop) for 
network IO.  And there's definitely no problem with async/await performance -- 
we're optimizing asyncio here, not the interpreter.

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

Yury, thank you very much for circling back. I wish I could be more helpful in 
pursuing performance improvements.

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[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

Liran,  Task (C implementation) was optimized in issue 32348; your benchmark 
now runs 15% faster.

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

> Also I suggest you to try uvloop

Sadly, uvloop does not offer any noticeable improvement in performance for us. 
Our usage is very similar to the "benchmarks" I posted - we don't do any actual 
async I/O because asynq does not offer that. 

> I suggest you to profile it and post real profiles here

Gladly! Would you like profiles of python within itself (as in, made with 
`cProfile`) or gmon.out profiles? the latter would be a little more difficult 
to run since we run a web server which needs to accept traffic, but I do have 
plenty of `cProfile` profiles I could share with you.

> I just don't think that asyncio.gather can be the main bottleneck you have, 
> it must be something else

I think my PR and the examples I have provided set a different mindset to this 
issue - the issue in question is that the "sync" performance of async/await is 
very poor when used to execute things in "sync". The benchmarks provided are an 
example of what a request life time looks like - there's a lot of 
scatter-gather to batch database queries that happen in sync (for the time 
being) which in the benchmark being simulated as simple math operations. To 
reiterate, I do not think `asyncio.gather` is the main performance bottleneck. 
I do not know how to better identify it with my limited knowledge about cpython.

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[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

Also I suggest you to try uvloop.  If your production code is still slower that 
with asynq, I suggest you to profile it and post real profiles here.  I just 
don't think that asyncio.gather can be the main bottleneck you have, it must be 
something else.

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[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

> I agree that the PR I offers little (or no) improvement but I implore you to 
> explore performance bottlenecks in async/await.

And I'm saying that there are no "performance bottlenecks in async/await".  
async/await is *not* asyncio.  async/await and yield are language constructs 
that use generator objects.

Your benchmark *does not* test async/await vs yield.  It compares 
asyncio.gather to batches in asynq.

Now, maybe asyncio.gather can be optimized, but we should open a separate issue 
for that if we can have a better implementation of it.

Your benchmark doesn't test the performance of IO -- that's the thing we 
actually optimize in asyncio and that we usually benchmark.  asyncio.gather is 
a niche thing, and usually network applications don't have it as a bottleneck.

Closing this issue.

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resolution:  -> not a bug
stage:  -> resolved
status: open -> closed

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

> which makes them faster in some specific micro-benchmarks

I'm not talking about micro-benchmarks, we are actively using asynq in 
production. Recent efforts to migrate to async/await have hit a major  
performance hit - our response times nearly doubled.

I agree that the PR I offers little (or no) improvement but I implore you to 
explore performance bottlenecks in async/await.

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[issue32204] async/await performance is very low

[Yury Selivanov]

Yury Selivanov  added the comment:

In general, implementing coroutines using 'yield' expressions (not 'yield 
from'!) is slower than async/await, because the former approach needs a 
trampoline to manage the stack, whereas CPython itself handles that for 'yield 
from' and 'await'.  I suspect that any difference in performance is not related 
to 'async/await' vs 'yield' performance.

The attached benchmarks compare two completely different frameworks: asyncio 
and asynq.  Both have different implementations of Task and Future and event 
loops primitives.  Perhaps both of them schedule IO events and callbacks 
differently as well.

asyncio could be slower because all tasks' callbacks must be scheduled through 
the event loop, whereas some frameworks like Twisted schedule them right away, 
which makes them faster in some specific micro-benchmarks.  Or there might be 
an issue with 'asyncio.gather()', which is stressed heavily in the attached 
benchmarks.

What I can say for sure, is that Python implementation of async/await has 
nothing to do with the results you observe.

I suggest to take a look at 'asyncio.gather', maybe we can make it faster.  
Please open a new issue if you find any ways to make it faster.

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[issue32204] async/await performance is very low

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

~3-5% difference is a random variance.

Add 1/0 in this method and repeat the benchmark.

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

The PR is merely a finding I ran into while benchmarking. In my executions I 
saw a consistent ~3-5% performance increase.

At my company we are attempting to migrate from asynq to asyncio but 
performance suffers (our servers response times nearly double). I personally 
ran profiles and benchmarks and noticed this tiny bottleneck which I knew how 
to fix, so I submitted a PR to the python project in hopes it helps.

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[issue32204] async/await performance is very low

[Serhiy Storchaka]

Change by Serhiy Storchaka :


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versions: +Python 3.7 -Python 3.6

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[issue32204] async/await performance is very low

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

I don't see any difference after applying PR 4186.

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[issue32204] async/await performance is very low

[Liran Nuna]

Liran Nuna  added the comment:

Added comparable benchmark in asynq

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Added file: https://bugs.python.org/file47314/batch_asynq.py

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[issue32204] async/await performance is very low

[Liran Nuna]

New submission from Liran Nuna :

The performance of async/await is very low when compared to similar code that 
implements similar functionality via iterators, such as Quora's asynq library 
(https://github.com/quora/asynq/tree/master/asynq).

Based on my benchmarks, asynq is almost twice as fast as async/await. 

I have found some performance hanging fruit when benchmarking (See attached 
GitHub PR).


$ time python batch_asyncio.py 

real0m5.851s
user0m5.760s
sys 0m0.088s
$ time python batch_asynq.py 

real0m2.999s
user0m2.900s
sys 0m0.076s

--
components: asyncio
files: batch_asyncio.py
messages: 307492
nosy: Liran Nuna, yselivanov
priority: normal
pull_requests: 4599
severity: normal
status: open
title: async/await performance is very low
type: performance
versions: Python 3.6
Added file: https://bugs.python.org/file47313/batch_asyncio.py

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