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gh-104144: Optimize gather to finish eagerly when all futures complete eagerly#104138

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kumaraditya303 merged 8 commits intopython:mainfromitamaro:asyncio-skip-gathering-future

May 6, 2023

Merged

gh-104144: Optimize gather to finish eagerly when all futures complete eagerly#104138

kumaraditya303 merged 8 commits intopython:mainfromitamaro:asyncio-skip-gathering-future

May 6, 2023

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itamaro commentedMay 3, 2023•
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gh-97696 introduced eager tasks factory, which speeds up some async-heavy workloads by up to 50% when opted in.

installing the eager tasks factory applies out-of-the-box when gathering futures (asyncio.gather(...)), e.g.:

asyncio.get_event_loop().set_task_factory(asyncio.eager_task_factory)await asyncio.gather(coro1, coro2, coro3)

coro{1,2,3} will eagerly execute the first step, and potentially complete without scheduling to the event loop if the coros don't block.

the implementation ofeager uses callbacks internally that end up getting scheduled to the event loop even if all the futures were able to finish synchronously, and blocking the coroutine in whichgather() was awaited, preventing the task from completing eagerly even if otherwise it could.

applications that use multiple levels of nested gathers can benefit significantly from eagerly completing multiple levels without blocking, as implemented in this PR by skipping scheduling done callbacks for futures that are already done (e.g. finished eagerly).

Benchmarks

this makes the async pyperformance benchmarks up to 3x faster (!!), using apatch to pyperformance that adds "eager" flavors

3.12-base.20230503.async.4.json===============================Performance version: 1.0.7Python version: 3.12.0a7+ (64-bit) revision da1980afcbReport on Linux-5.15.0-1033-aws-x86_64-with-glibc2.31Number of logical CPUs: 72Start date: 2023-05-03 23:27:23.329046End date: 2023-05-03 23:46:37.7063263.12-nogf.20230503.async.2.json===============================Performance version: 1.0.7Python version: 3.12.0a7+ (64-bit) revision 5397cd9f62Report on Linux-5.15.0-1033-aws-x86_64-with-glibc2.31Number of logical CPUs: 72Start date: 2023-05-03 23:05:45.011427End date: 2023-05-03 23:22:44.908094+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| Benchmark                     | 3.12-base.20230503.async.4.json | 3.12-nogf.20230503.async.2.json | Change       | Significance           |+===============================+=================================+=================================+==============+========================+| async_tree_cpu_io_mixed       | 868 ms                          | 859 ms                          | 1.01x faster | Not significant        |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_eager              | 391 ms                          | 129 ms                          | 3.03x faster | Significant (t=209.74) |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_eager_cpu_io_mixed | 756 ms                          | 490 ms                          | 1.54x faster | Significant (t=167.41) |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_eager_io           | 1.51 sec                        | 1.50 sec                        | 1.00x faster | Not significant        |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_eager_memoization  | 595 ms                          | 314 ms                          | 1.89x faster | Significant (t=70.25)  |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_io                 | 1.39 sec                        | 1.40 sec                        | 1.00x slower | Not significant        |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_memoization        | 677 ms                          | 683 ms                          | 1.01x slower | Not significant        |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+| async_tree_none               | 575 ms                          | 574 ms                          | 1.00x faster | Not significant        |+-------------------------------+---------------------------------+---------------------------------+--------------+------------------------+

Issue:Leverage eager tasks to optimize asyncio gather & TaskGroups further #104144

AlexWaygood added the topic-asyncio label

May 3, 2023

gh-NNNN: Skip creating GatheringFuture if all futures finished eagerly

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itamaro force-pushed theasyncio-skip-gathering-future branch from4a5d42c tob3e479aCompare

May 3, 2023 20:57

itamaro changed the title~~gh-NNNN: Skip creating GatheringFuture if all futures finished eagerly~~gh-104144: Skip creating GatheringFuture if all futures finished eagerly

May 3, 2023

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May 3, 2023

Leverage eager tasks to optimize asyncio gather & TaskGroups further#104144

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itamaro marked this pull request as ready for review

May 3, 2023 23:52

itamaro requested review from1st1,asvetlov,gvanrossum,kumaraditya303 andwillingc ascode owners

May 3, 2023 23:52

carljm reviewed

May 4, 2023

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This looks pretty straightforward and reasonable to me, but would prefer for asyncio experts to take a look.

Misc/NEWS.d/next/Library/2023-05-03-16-50-24.gh-issue-104144.yNkjL8.rst OutdatedShow resolvedHide resolved

Apply review suggestion to NEWS entry

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Co-authored-by: Carl Meyer <carl@oddbird.net>

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If you look atgather._done_callback() you'll see it has a bunch of logic which gets executed at the moment all the futures have finished (starting fromif nfinished == nfuts: on line 781). If all args can complete eagerly then this will be executed eagerly too.

This might have a few issues:

At this pointouter will beNone and this will cause trouble on line 803. (Maybe I missed something because I'm surprised this hasn't come up yet).
Handling for futures that were cancelled during eager execution is processed but the results discarded.
We inefficiently create a result list which we discard and then repeat when creating the eagerly completed future result.

Fortunately, Ithink an easy fix is to move creation of the eager result future to before the argument processing loop. See my in-line comments for specifics.

I'm not 100% sure how this will affect the issue described inbpo-46672, but it has a test so we'll see.

Lib/asyncio/tasks.py OutdatedShow resolvedHide resolved

Lib/asyncio/tasks.py Outdated

		outer=futures.Future(loop=loop)
		outer.set_result([c.resultforcinchildren])
		else:
		outer=_GatheringFuture(children,loop=loop)

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Suggested change

	outer=_GatheringFuture(children,loop=loop)
	outer.__self_log_traceback=False
	outer=_GatheringFuture(children,loop=loop)

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May 4, 2023

itamaro added2 commits

May 5, 2023 11:50

Merge branch 'main' into asyncio-skip-gathering-future

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Modify implementation to eagerly call done callbacks at the end of th…

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…e loop, after the GatheringFuture (outer) is created

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carljm commentedMay 5, 2023

The title no longer accurately describes the updated PR, since the_GatheringFuture is always created.

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itamaro commentedMay 5, 2023

thanks for the review@jbower-fb !

I pushed a new version of the PR based on your suggestions, but not identical.
summary of my changes:

instead of immediately calling the done callbacks for eagerly completed futures in the loop, I add them to a list and call their callbacks only at the end, after creating the outer future
this helps because now outer is defined the same way, and the children list is fully populated, which is also important because the done callback uses the children list
I always create a GatheringFuture so I get the same cancellation treatment, but it will still finish eagerly if all futures completed eagerly thanks to the last done callback right before returning
there shouldn't be any issues withbpo-46672 since outer looks the same as before

itamaro changed the title~~gh-104144: Skip creating GatheringFuture if all futures finished eagerly~~gh-104144: Optimize gather to finish eagerly when all futures complete eagerly

May 5, 2023

bedevere-bot added awaiting review and removed awaiting core review labels

May 5, 2023

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itamaro commentedMay 5, 2023

The title no longer accurately describes the updated PR, since the_GatheringFuture is always created.

thanks, I updated the title!

itamaro added2 commits

May 5, 2023 14:14

update inline comment and NEWS entry

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Merge branch 'main' into asyncio-skip-gathering-future

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May 6, 2023

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LGTM, will fix the typo. Maybe@carljm can merge when you all are agreed on this. Nice fix!

Misc/NEWS.d/next/Library/2023-05-03-16-50-24.gh-issue-104144.yNkjL8.rst OutdatedShow resolvedHide resolved

bedevere-bot added awaiting merge and removed awaiting review labels

May 6, 2023

Fix NEWS typo

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AlexWaygood added the performancePerformance or resource usage label

May 6, 2023

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gvanrossum commentedMay 6, 2023

PS. Ingeneral there's no need to click the "Update branch" button (or otherwise merge main back into the PR)unless there are fixes/changes that might affect the PR (e.g. if touching the same file).