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From: | Dmitry Gutov |
Subject: | bug#24048: 25.0.95; syntax-ppss can be slow |
Date: | Mon, 25 Jul 2016 04:16:45 +0300 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:47.0) Gecko/20100101 Thunderbird/47.0 |
Hi Aaron, On 07/21/2016 05:29 PM, Aaron Jensen wrote:
In certain situations, the caching of syntax-ppss can seem to be insufficient for good performance when syntax-ppss is invoked in a tight loop. smartparens is a popular package that currently invokes syntax-ppss in a tight loop (about 30-100 times depending on how many match pairs are configured). syntax-ppss has caching built in, but it is willing to use a cache from a further back position and do a `parse-partial-sexp` from the old position to the current. Afterwards, it does not set the cache with the current position. As such, in the pathological case, it can parse ~2000 characters 30-100 times in a tight loop. This is slow enough to show up in profiling and affect typing latency. To repro, install: smartparens (you can use https://github.com/aaronjensen/smartparens/tree/limit-binding-of-case-fold-search to alleviate a different performance issue which could distract in the profiling) elixir-mode
Is there a way to reproduce it more easier? Maybe without smartparens, just with elixir-mode, if it's sufficient to illustrate the performance problem (I recall you stating parse-partial-sexp is also unusually slow in that major mode, for some reason).
Here, I'm seeing some similar behavior with elisp-mode.el. I can open this file, evaluate
(benchmark 1000 '(syntax-ppss))at line 10, then move to line 70 and do it there, and see the latter result to be much faster. They're still below 100ms usually (even with 1000 repetitions), so that's hardly a good example of a performance problem, by itself.
P.S. Please send a text email next time, we very much prefer them for various reasons, inability to sneak in a tracker like this among them:
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