GNU bug report logs - #79116
31.0.50; Crash on IGC build

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Message #83 received at 79116 <at> debbugs.gnu.org (full text, mbox):

From: Eli Zaretskii <eliz <at> gnu.org>
To: Helmut Eller <eller.helmut <at> gmail.com>
Cc: gerd.moellmann <at> gmail.com, spd <at> toadstyle.org, pipcet <at> protonmail.com,
 79116 <at> debbugs.gnu.org
Subject: Re: bug#79116: 31.0.50; Crash on IGC build
Date: Fri, 01 Aug 2025 15:28:28 +0300

> From: Helmut Eller <eller.helmut <at> gmail.com>
> Cc: gerd.moellmann <at> gmail.com,  spd <at> toadstyle.org,  pipcet <at> protonmail.com,
>   79116 <at> debbugs.gnu.org
> Date: Fri, 01 Aug 2025 13:44:08 +0200
> 
> >> If there aren't any Lisp objects involved, then there is no problem.
> >> The problematic cases are (or could be) structs that are malloc'd and
> >> contain references to GC-managed objects.
> >
> > What is a "GC-managed object", for this purpose?  How can one
> > determine whether a given object is or isn't GC-managed?
> 
> Objects that allocated on the GC heap and automatically freed are
> GC-managed.

That answers the first question I asked, but not the second one, which
is what is important in practice.

> >> Yes, it would require more work during the root scanning phase.
> >> 
> >> However, performance of igc is already unconvincing: throughput with the
> >> old GC and gc-cons-percentage = 1.0 is better than with igc.
> >
> > Did you try to run interactively with gc-cons-percentage = 1.0?  If
> > you did, can you share the experience?
> 
> No.  I usually run igc with an MPS debug build; it has much longer and
> noticeable GC pauses than a regular built.
> 
> However, I have a bunch of benchmarks and those are executed inside GNU
> screen [*].  I don't claim that the benchmarks are good or relevant or
> anything.  For the longest time I didn't even know that batch mode uses
> a different gc-cons-percentage.  Doh!  The results, with all its
> badness, are:

The "real" data seems to contradict what both Gerd and myself see in
interactive usage: the pause times, such as they are, in the igc
branch are significantly shorter, almost as if they didn't exist.

> > My anecdotal evidence from running the igc branch is unambiguous: it
> > is significantly less "stuttering" than the master branch.
> 
> Is that with gc-cons-percentage = 0.1?

I compare "emacs -Q", so yes.

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