[New-bugs-announce] [issue16876] epoll: reuse epoll_event buffer instead of allocating a new one at each poll()

[Charles-François Natali]

New submission from Charles-François Natali:

Currently, epoll.poll() allocates an epoll_event buffer every time/ this is bad, because it changes an O(number of ready FDs) syscall into a O(maxevents/FD_SETSIZE) complexity.
The patch attached allocates a epoll events buffer per epoll instance, and it only gets reallocated when necessary (note that the reallocation heuristic will probably be improved in #16873 (and having a per instance maxevents count will likely be useful).

Here's a benchmark without patch:
$ ./python -m timeit -s 'import select; ep = select.epoll(); ep.register(1, select.EPOLLOUT)' 'ep.poll()'
100000 loops, best of 3: 4.25 usec per loop

With patch:
$ ./python -m timeit -s 'import select; ep = select.epoll(); ep.register(1, select.EPOLLOUT)' 'ep.poll()'
100000 loops, best of 3: 3.38 usec per loop

----------
components: Extension Modules
files: epoll_realloc.diff
keywords: needs review, patch
messages: 179167
nosy: neologix
priority: normal
severity: normal
stage: patch review
status: open
title: epoll: reuse epoll_event buffer instead of allocating a new one at each poll()
type: performance
versions: Python 3.4
Added file: http://bugs.python.org/file28585/epoll_realloc.diff

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue16876>
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