bug#26525: `sit-for' in Flyspell slows typing down, hogs 90% of CPU

[Damien Cassou]

I have attached a profile in which Flyspell's flyspell-check-word-p
consumes 89% of CPU time while typing text in a buffer. […]

This happened to me in the past then stopped for months. Now it happens
again and is really annoying. Emacs regularly freezes for around 5
seconds when I manipulate text.

[Stefan Kangas]

Thanks! I don't expect that this feature is intended to slow down typing, though, right? In the example I posted it makes typing painfully slow.

I didn't see any example in your OP, only a profile. What did I miss?
And no, this is not supposed to slow down typing in any significant
way, as long as you type, because sit-for is supposed to return as
soon as input is available. Your complaint was about CPU usage, not
about time delays, AFAIU.

Indeed, there was only a profile; I don't have a good repro yet. In that case, flyspell was slowing things down a lot, and the complaint was indeed about delays.
Sorry for being unclear.

That was 3 years ago. Are you still seeing this on a recent version of
Emacs, such as the recently released 27.1?

Best regards,
Stefan Kangas

[Stefan Kangas]

Post by Damien Cassou

I have attached a profile in which Flyspell's flyspell-check-word-p
consumes 89% of CPU time while typing text in a buffer. […]

This happened to me in the past then stopped for months. Now it happens
again and is really annoying. Emacs regularly freezes for around 5
seconds when I manipulate text.

That was 3 years ago. Are you still seeing this on a recent version of
Emacs, such as the recently released 27.1?

Best regards,
Stefan Kangas

[Damien Cassou]

Post by Stefan Kangas
That was 3 years ago. Are you still seeing this on a recent version of
Emacs, such as the recently released 27.1?

This hasn't happened for some time.

[Clément Pit-Claudel]

Post by Damien Cassou

Post by Stefan Kangas
That was 3 years ago. Are you still seeing this on a recent version of
Emacs, such as the recently released 27.1?

This hasn't happened for some time.

There was a report of a similar issue on reddit recently, but it hasn't happened to me of late.

[Stefan Kangas]

tags 26525 + unreproducible
thanks

Post by Clément Pit-Claudel

Post by Damien Cassou

Post by Stefan Kangas
That was 3 years ago. Are you still seeing this on a recent version of
Emacs, such as the recently released 27.1?

This hasn't happened for some time.

There was a report of a similar issue on reddit recently, but it hasn't happened to me of late.

You wouldn't happen to have a link to the relevant thread? I tried
searching the web but couldn't find anything.

I'm marking this bug as unreproducible for now. Please report back if
you see this again or can provide any more information.

[Clément Pit-Claudel]

Post by Stefan Kangas
You wouldn't happen to have a link to the relevant thread? I tried
searching the web but couldn't find anything.

https://www.reddit.com/r/emacs/comments/i96lbo/flyspell_consuming_most_of_my_resources_why_oo/ , sorry for not including it the first time.

[Nick H]

Post by Stefan Kangas
I'm marking this bug as unreproducible for now. Please report back
if you see this again or can provide any more information.

I just bumped into this bug on 27.1 with the same symptoms - typing lag
after activating flyspell-mode.

I took a couple of profiles - the first when lag was apparent and
another after clearing the lag by toggling flyspell-mode.

Both profiles show a similar result, so the "high cpu" in sit-for might
be a red-herring.

Profile 1 - with lag
- flyspell-post-command-hook 1146 92%
- flyspell-check-word-p 1120 90%
- sit-for 1117 90%
- redisplay 551 44%
+ redisplay_internal (C function) 1 0%
read-event 390 31%
- flyspell-get-not-casechars 1 0%
ispell-get-decoded-string 1 0%
+ flyspell-word 8 0%
+ flyspell-check-pre-word-p 3 0%
+ command-execute 65 5%
+ ... 22 1%
+ undo-auto--add-boundary 1 0%

Profile 2 - without lag
- flyspell-post-command-hook 3507 94%
- flyspell-check-word-p 3432 92%
- sit-for 3414 92%
- redisplay 1660 44%
+ redisplay_internal (C function) 3 0%
+ read-event 1317 35%
+ ispell-get-otherchars 6 0%
+ flyspell-get-not-casechars 5 0%
+ flyspell-word 17 0%
+ flyspell-check-pre-word-p 13 0%
+ command-execute 93 2%
+ ... 87 2%
+ timer-event-handler 3 0%
undo-auto--add-boundary 2 0%
tooltip-hide 1 0%

Nick

[Stefan Kangas]

Post by Nick H
I just bumped into this bug on 27.1 with the same symptoms - typing lag
after activating flyspell-mode.

What is your ispell/flyspell configuration?

Do you have any ideas about how to reproduce it, or could you say
something about the circumstances under which you saw this?