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bug#49127: Performance degradation in encode_coding_object
From: |
Eli Zaretskii |
Subject: |
bug#49127: Performance degradation in encode_coding_object |
Date: |
Sun, 25 Jul 2021 10:10:40 +0300 |
Ping! Ping! Please respond, so we could take care of this issue.
To recap: I would like to have a backtrace from the call to
encode_coding_object, including the Lisp backtrace (via the
"xbacktrace" command), so that we could see how this performance issue
happens.
TIA
> Date: Thu, 24 Jun 2021 19:49:41 +0300
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 49127@debbugs.gnu.org
>
> Ping! Could you please respond to my requests below? I'd like to
> make some progress with this bug report.
>
> > Date: Sun, 20 Jun 2021 12:04:59 +0300
> > From: Eli Zaretskii <eliz@gnu.org>
> > Cc: 49127@debbugs.gnu.org
> >
> > > Date: Sun, 20 Jun 2021 08:30:24 +0200
> > > From: Victor Nawothnig via "Bug reports for GNU Emacs,
> > > the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>
> > >
> > > With gprof/prof_events I have nailed the problem to be
> > > encode_coding_object looping over all markers. In degenerate cases this
> > > list can contain millions of markers. Traversing this list is
> > > particularly slow because of the indirection being a singly linked list.
> > > Based on the fact that a GC remedies this, I’m assuming this list
> > > contains mostly unreachable markers. When stepping through
> > > encode_coding_object with GDB after a GC this list of markers shrinks to
> > > small double digit numbers from millions.
> > >
> > > The source of these markers appears to be looking-at in the font locking
> > > code of haskell-mode, this assumption is based on the fact that
> > > commenting out the uses of looking-at in haskell-mode prevents the
> > > accumulation of markers and thus the slowdown.
> >
> > Do you understand why using looking-at causes creation of markers? If
> > so, can you show the details of why this happens?
> >
> > > One contributing factor to all of this, is that for lsp-mode to perform
> > > adequately, one needs a relatively high gc-cons-threshold, which means
> > > GCs that would clean up the markers run more rarely, leading to higher
> > > accumulation of markers over time.
> >
> > Yes, playing with GC threshold is usually a bad idea, but it is hard
> > to explain to people why, and they keep doing that, to their cost.
> >
> > > This problem only triggers in terminal frames, but not in GUI frames.
> > > Setting GDB breakpoints suggests that the GUI frame never even calls into
> > > encode_coding_object.
> >
> > Can you should a backtrace from the call to encode_coding_object,
> > including the Lisp backtrace (via the "xbacktrace" command)?
> >
> > > So far I’m torn on whether this is a bug in the haskell-mode font locking
> > > code or in Emacs. What do you think?
> >
> > Let's revisit this question after we have all the data I requested
> > above, okay?
> >
> > Thanks.
> >
> >
> >
> >
>
>
>
>
>
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