Multiple high CPU eqwalizer tasks and emacs freezing

[tsloughter]

Describe the bug

I was waiting to open this until I had more info but I've not had time to dig in simple checks and wanted to get this open in case anyone else knows how/where I should look.

The issue is frequently seeing processes like eqwalizerkiPIC5 at 100% cpu and emacs hangs for a few seconds. The hanging doesn't happen every time I see a process at 100% and sometimes the process has arguments, like:

 /tmp/eqwalizerkiPIC5 ipc opentelemetry_exporter_metrics_service_pb  

That file is large, 5980 lines, and open in a buffer but not the one I'll be editing when this happens.

To Reproduce

Not entirely sure but it happens on https://github.com/open-telemetry/opentelemetry-erlang and may be tied to having files like https://github.com/open-telemetry/opentelemetry-erlang/blob/main/apps/opentelemetry_exporter/src/opentelemetry_exporter_metrics_service_pb.erl

Expected behavior

To not constantly see processes at 100%, even when nothing has changed. At the moment I haven't editted anything in minutes but have 3 eqwalizerkiPIC5 processes at 200% cpu.

Actual behavior

Frequent freezing of emacs and, even when not frozen, constant eqwalizer processes using high cpu.

Context

• ELP Version (output of elp version): 1.1.0+build-2024-01-29
• Editor used: emacs 29.2.50

[alanz]

We have a known problem of performance with generated protobuf files.

A workaround in the meantime is to disable eqwalizer for the specific file by adding -eqwalizer(ignore). to the top of the file, or to add a @generated tag in the first 2000 characters of the file.

[tsloughter]

Thanks! Should I leave this open or close it?

[alanz]

Leave it open, we are looking at ways of adding config to control the eqwalizer resource usage, which will happen against this issue.

[tomas-abrahamsson]

... or to add a @generated tag in the first 2000 characters of the file.

Will ELP pick up @generated even if it does not appear first on a (comment) line? I'm trying to find a way to say @generated that doesn't "upset" edoc.

$ cat a.erl
%% this file is @generated
-module(a).
$ cat b.erl                                                            
%% @doc example
%% @generated
-module(b).
$ 
$ erl -noinput -eval 'erlang:display(edoc:file("a.erl", [])), halt(0).' 
ok
$ erl -noinput -eval 'erlang:display(edoc:file("b.erl", [])), halt(0).'
b.erl, in module header: at line 2: warning: tag @generated not recognized.
ok
$ 

[alanz]

We just look for the presence of it in the first 2000 chars. see https://github.com/WhatsApp/erlang-language-platform/blob/425a5dadf249541a5484a51fdc03f5401cfa7056/crates/base_db/src/lib.rs#L210

The edoc manual suggests doing

% % @doc ...

[alanz]

We have also added the ability to set how many eqwalizer instances should run, in the .elp.toml file.

But you must build from source or wait for the next release to be able to use it.

[tsloughter]

Thanks for the quick release @tomas-abrahamsson

But @alanz I just regenerated the files with the added @generated and restarted emacs to be sure but still see the process popping up. I'm now on elp version 1.1.0+build-2024-02-16 and see:

/tmp/eqwalizeruo4hT2 ipc opentelemetry_exporter_metrics_service_pb

despite the top of that file being:

%% -*- coding: utf-8 -*-
%% % this file is @generated
%% @private
%% Automatically generated, do not edit
%% Generated by gpb_compile version 4.21.1
%% Version source: file
-module(opentelemetry_exporter_metrics_service_pb).

[alanz]

We have been looking at the code, and requesting types on hover does not honour the @generated tag. It probably makes sense to have it do so.

In the meantime, can you do an experiment and add -eqwalizer(ignore). to the generated file (by hand), and see if anything changes?

[tsloughter]

Ah yea, just did and it looks like it may have done it. I'd say I need to use it longer to be positive but I was seeing those processes immediately before adding the module attribute and now they are gone.

[alanz]

Ok, we will make the change for types on hover not to do generated.

[alanz]

I think this is done now, will close.

The new release should also make things more stable.