[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Change by Inada Naoki :


--
resolution:  -> fixed
stage: patch review -> resolved
status: open -> closed

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Inada Naoki  added the comment:


New changeset 9a7e5b1b42abcedb895b1ce49d83fe067d01835c by Inada Naoki in branch 
'master':
bpo-35279: reduce default max_workers of ThreadPoolExecutor (GH-13618)
https://github.com/python/cpython/commit/9a7e5b1b42abcedb895b1ce49d83fe067d01835c


--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Change by Inada Naoki :


--
keywords: +patch
pull_requests: +13520
stage:  -> patch review
pull_request: https://github.com/python/cpython/pull/13618

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Andrew Svetlov]

Andrew Svetlov  added the comment:

> how about min(32, cpu_count+4)?

I think it produces reasonable good numbers for any CPU count.

Do you have time for preparing a pull request?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Inada Naoki  added the comment:

> If you want to limit to 16-20 that may be ok but `cpu_count + 4` doesn't work 
> in this case. On cloud servers, I see 128 or even more cores very often. 
> 160+4 is not that you want to propose, sure.


I proposed cpu_count + 4 because #24882 almost fixed the problem of large 
maxworks.
If you don't like it, how about min(32, cpu_count+4)?


> I insist on changing the default calculation schema in concurrent.futures, 
> not in asyncio. There is no case for asyncio to be exceptional.

Makes sense.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Andrew Svetlov]

Andrew Svetlov  added the comment:

I'm ok with changing the default threads number limit.
Not sure about numbers.
If you want to limit to 16-20 that may be ok but `cpu_count + 4` doesn't work 
in this case. On cloud servers, I see 128 or even more cores very often. 160+4 
is not that you want to propose, sure.

I insist on changing the default calculation schema in concurrent.futures, not 
in asyncio. There is no case for asyncio to be exceptional.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Inada Naoki  added the comment:

Current default value is decided in here:
https://bugs.python.org/review/21527/#ps11902

It seems there were no strong reason for current cpu_count * 5.
I think cpu_count + 4 is better default value, because:

* When people are using threadpool for CPU heavy job which releases GIL, 
workers >= cpu_count is good.
* When people are using threadpool for multiplexing I/O, best workers number is 
vary on the workload.  But I think 4~16 is good for typical case.



> This is amplified by the fact that the 
> `concurrent.futures.ThreadPoolExecutor` threads are never killed, and are not 
> re-used until `max_workers` threads are spawned.

Note that this is fixed by #24882.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Andrew Svetlov]

Andrew Svetlov  added the comment:

asyncio uses bare concurrent.futures.ThreadPoolExecutor.
Tha question is: should asyncio reduce the number of threads in the pool or 
concurrent.futures should change the default value?

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Inada Naoki  added the comment:

node.js default threadpool size is 4 regardless number of cores.
https://nodejs.org/api/cli.html#cli_uv_threadpool_size_size

Since we has GIL, I think fixed-size pool is better idea.

--

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Laurie Opperman]

Laurie Opperman  added the comment:

What about making it dependant on memory as well as logical processor count:

`n_workers = min(RAM_GB / some_number, N_CORES * 5)`

--
nosy: +Epic_Wink

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Inada Naoki]

Change by Inada Naoki :


--
nosy: +inada.naoki

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com

[issue35279] asyncio uses too many threads by default

[Vojtěch Boček]

New submission from Vojtěch Boček :

By default, asyncio spawns as many as os.cpu_count() * 5 threads to run I/O on. 
When combined with beefy machines (e.g. kubernetes servers) with, says, 56 
cores, it results in very high memory usage.

This is amplified by the fact that the `concurrent.futures.ThreadPoolExecutor` 
threads are never killed, and are not re-used until `max_workers` threads are 
spawned.

Workaround:


loop.set_default_executor(concurrent.futures.ThreadPoolExecutor(max_workers=8))

This is still not ideal as the program might not need max_workers threads, but 
they are still spawned anyway.

I've hit this issue when running asyncio program in kubernetes. It created 260 
idle threads and then ran out of memory.

I think the default max_workers should be limited to some max value and 
ThreadPoolExecutor should not spawn new threads unless necessary.

--
components: asyncio
messages: 330101
nosy: Vojtěch Boček, asvetlov, yselivanov
priority: normal
severity: normal
status: open
title: asyncio uses too many threads by default
type: resource usage
versions: Python 3.7

___
Python tracker 

___
___
Python-bugs-list mailing list
Unsubscribe: 
https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com