New submission from Larry Hastings <la...@hastings.org>:
This patch was sent to me privately by Jeethu Rao at Facebook. It's a change
they're working with internally to improve startup time. What I've been told
by Carl Shapiro at Facebook is that we have their blessing to post it publicly
/ merge it / build upon it for CPython. Their patch was written for 3.6, I
have massaged it to the point where it minimally works with 3.8.
What the patch does: it takes all the Python modules that are loaded as part of
interpreter startup and deserializes the marshalled .pyc file into precreated
objects stored as static C data. You add this .C file to the Python build.
Then there's a patch to Python itself (about 250 lines iirc) that teaches it to
load modules from these data structures.
I wrote a quick dumb test harness to compare this patch vs 3.8 stock. It runs
a command line 500 times and uses time.perf_counter to time the process. On a
fast quiescent laptop I observe a 21-22% improvement:
cmdline: ['./python', '-c', 'pass']
500 runs:
sm38
average time 0.006302303705982922
best 0.006055746000129147
worst 0.00816565500008437
clean38
average time 0.007969956444008858
best 0.007829047999621253
worst 0.008812210000542109
improvement 0.20924239043734505 %
cmdline: ['./python', '-c', 'import io']
500 runs:
sm38
average time 0.006297688038004708
best 0.005980765999993309
worst 0.0072462130010535475
clean38
average time 0.007996319670004595
best 0.0078091849991324125
worst 0.009175700999549008
improvement 0.21242667903482038 %
The downside of the patch: for these modules it ignores the Python files on
disk--it doesn't even stat them. If you add stat calls you lose half of the
speed improvement. I believe they added a work-around, where you can set a
flag (command-line? environment variable? I don't know, I didn't go looking for
it) that tells Python "don't use the frozen modules" and it loads all those
files from disk.
I don't propose to merge the patch in its current state. I think it would need
a lot of work both in terms of "doing things the way Python does it" as well as
just code smell (the serializer is implemented in both C and Python and jumps
back and forth, also the build process for the serialized modules is pretty
tiresome).
Is it worth working on?
----------
assignee: larry
components: Interpreter Core
messages: 325401
nosy: larry
priority: normal
severity: normal
stage: needs patch
status: open
title: Store startup modules as C structures for 20%+ startup speed improvement
type: enhancement
versions: Python 3.8
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Python tracker <rep...@bugs.python.org>
<https://bugs.python.org/issue34690>
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