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Implement zero copy writes in SelectorSocketTransport in asyncio #91166Description
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GitHub fields:
assignee = None
closed_at = None
created_at = <Date 2022-03-14.09:18:41.974>
labels = ['3.11', 'expert-asyncio', 'performance']
title = 'Implement zero copy writes in SelectorSocketTransport in asyncio'
updated_at = <Date 2022-03-21.23:44:35.077>
user = 'https://github.com/kumaraditya303' bugs.python.org fields:
activity = <Date 2022-03-21.23:44:35.077>
actor = 'jakirkham'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['asyncio']
creation = <Date 2022-03-14.09:18:41.974>
creator = 'kumaraditya'
dependencies = []
files = []
hgrepos = []
issue_num = 47010
keywords = ['patch']
message_count = 2.0
messages = ['415124', '415131']
nosy_count = 5.0
nosy_names = ['gvanrossum', 'asvetlov', 'yselivanov', 'jakirkham', 'kumaraditya']
pr_nums = ['31871']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'resource usage'
url = 'https://bugs.python.org/issue47010'
versions = ['Python 3.11'] Activitykumaraditya303 commented on Mar 14, 2022 ContributorAuthor More actions Currently, _SelectorSocketTransport transport creates a copy of the data before sending which in case of large amount of data, can create multiple giga bytes copies of data before sending.
Script demonstrating current behavior:
import asyncio
import memory_profiler
@memory_profiler.profile
async def handle_echo(reader: asyncio.StreamReader, writer: asyncio.StreamWriter):
data = b'x' * 1024 * 1024 * 1000 # 1000 MiB payload
writer.write(data)
await writer.drain()
writer.close()
async def main():
server = await asyncio.start_server(
handle_echo, '127.0.0.1', 8888)
addrs = ', '.join(str(sock.getsockname()) for sock in server.sockets)
print(f'Serving on {addrs}')
async with server:
asyncio.create_task(server.start_serving())
reader, writer = await asyncio.open_connection('127.0.0.1', 8888)
while True:
data = await reader.read(1024 * 1024 * 100)
if not data:
break
asyncio.run(main())Memory profile result:
Filename: test.py
Line # Mem usage Increment Occurrences Line Contents
=============================================================
4 17.7 MiB 17.7 MiB 1 @memory_profiler.profile
5 async def handle_echo(reader: asyncio.StreamReader, writer: asyncio.StreamWriter):
6 1017.8 MiB 1000.1 MiB 1 data = b'x' * 1024 * 1024 * 1000 bpo-1000 MiB payload
7 2015.3 MiB 997.5 MiB 1 writer.write(data)
8 2015.3 MiB -988.1 MiB 2 await writer.drain()
9 1027.1 MiB -988.1 MiB 1 writer.close()
------------------------------------------------------------------------
To make it zero copy, python's buffer protocol can be used and use memory views of data to save RAM. The writelines method currently joins all the data before sending whereas it can use socket.sendmsg to make it more memory efficient.
Links:
asvetlov commented on Mar 14, 2022 Known problem, PR is welcome!
I expect the fix is not trivial. kumaraditya303 commented on Oct 24, 2022 ContributorAuthor More actions New benchmark comparing various chunk and packet sizes:
import asyncio
from pyperf import Runner
async def handle_echo(reader: asyncio.StreamReader, writer: asyncio.StreamWriter, chunks: int, packet_size: int):
data = b'x' * packet_size
for _ in range(chunks):
writer.write(data)
await writer.drain()
writer.close()
await writer.wait_closed()
async def main(chunks: int, packet_size: int):
server = await asyncio.start_server(
lambda reader, writer: handle_echo(reader, writer, chunks, packet_size), '127.0.0.1', 8882)
async with server:
asyncio.create_task(server.start_serving())
reader, writer = await asyncio.open_connection('127.0.0.1', 8882)
while True:
data = await reader.read(packet_size)
if not data:
break
writer.close()
await writer.wait_closed()
if __name__ == '__main__':
runner = Runner()
for chunks in [10, 100]:
for packet_size in [1024, 1024 ** 2, 1024 ** 2 * 10]:
runner.bench_async_func(
f'echo {chunks} -- {packet_size}', main, chunks, packet_size)Fallback implementation with send:
| Benchmark |
base |
send |
| echo 10 -- 1024 |
1.11 ms |
951 us: 1.16x faster |
| echo 10 -- 1048576 |
12.3 ms |
9.89 ms: 1.24x faster |
| echo 10 -- 10485760 |
165 ms |
80.9 ms: 2.04x faster |
| echo 100 -- 1024 |
1.51 ms |
1.56 ms: 1.03x slower |
| echo 100 -- 1048576 |
98.6 ms |
81.0 ms: 1.22x faster |
| echo 100 -- 10485760 |
1.31 sec |
764 ms: 1.72x faster |
| Geometric mean |
(ref) |
1.35x faster |
Faster Implementation with sendmsg:
| Benchmark |
base |
sendmsg |
| echo 10 -- 1024 |
1.11 ms |
924 us: 1.20x faster |
| echo 10 -- 1048576 |
12.3 ms |
9.34 ms: 1.32x faster |
| echo 10 -- 10485760 |
165 ms |
77.7 ms: 2.12x faster |
| echo 100 -- 1024 |
1.51 ms |
1.58 ms: 1.05x slower |
| echo 100 -- 1048576 |
98.6 ms |
74.5 ms: 1.32x faster |
| echo 100 -- 10485760 |
1.31 sec |
717 ms: 1.83x faster |
| Geometric mean |
(ref) |
1.41x faster |
Memory usage:
| Benchmark |
base-memory |
sendmsg-memory |
| echo 10 -- 1048576 |
14.9 MB |
13.8 MB: 1.08x faster |
| echo 10 -- 10485760 |
47.7 MB |
22.8 MB: 2.09x faster |
| echo 100 -- 1048576 |
15.2 MB |
13.7 MB: 1.10x faster |
| echo 100 -- 10485760 |
51.6 MB |
22.9 MB: 2.25x faster |
| Geometric mean |
(ref) |
1.33x faster |
Benchmark hidden because not significant (2): echo 10 -- 1024, echo 100 -- 1024
The new implementation is faster on both send and sendmsg across the board with #31871 and avoids memory copying so "zero copy writes". kumaraditya303 commented on Dec 23, 2022 ContributorAuthor More actions Just for fun I ran the benchmark against uvloop and with my implementation asyncio either meets or beats uvloop by small margin. This is great considering that my PR does not involves C code or any third party libraries. gvanrossum commented on Dec 23, 2022 added a commit that references this issue on Dec 24, 2022GH-91166: Implement zero copy writes for `SelectorSocketTransport` in…
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