Re: The Emacs master is much slower than the emacs-27 branch.

[Stephen Berman]

On Fri, 04 Dec 2020 20:51:52 +0200 Eli Zaretskii <eliz@gnu.org> wrote:

>> From: Óscar Fuentes <ofv@wanadoo.es>
>> Date: Fri, 04 Dec 2020 17:28:36 +0100
>> 
>> Stephen Berman <stephen.berman@gmx.net> writes:
>> 
>> > emacs-27:
>> >
>> > system-configuration-options
>> > "'CFLAGS=-Og -g3' PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig"
>> >
>> > system-configuration-features
>> > "XPM JPEG TIFF GIF PNG RSVG SOUND DBUS GSETTINGS GLIB NOTIFY INOTIFY ACL
>> > GNUTLS LIBXML2 FREETYPE HARFBUZZ XFT ZLIB TOOLKIT_SCROLL_BARS GTK3 X11
>> > XDBE XIM MODULES THREADS LIBSYSTEMD PDUMPER LCMS2 GMP"
>> >
>> > master:
>> >
>> > system-configuration-options
>> > "--with-xwidgets 'CFLAGS=-Og -g3' PKG_CONFIG_PATH=/opt/qt5/lib/pkgconfig"
>> >
>> > system-configuration-features
>> > "XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND DBUS GSETTINGS GLIB NOTIFY
>> > INOTIFY ACL GNUTLS LIBXML2 FREETYPE HARFBUZZ ZLIB TOOLKIT_SCROLL_BARS
>> > GTK3 X11 XDBE XIM MODULES THREADS XWIDGETS LIBSYSTEMD PDUMPER LCMS2"
>> 
>> Please correct me if I'm wrong, but overriding CFLAGS means that gcc
>> compiles with default optimization level, wich is -O0, hence you are
>> comparing unoptimized builds, right?
>
> No, because CFLAGS say -Og in both cases, which means the compiler
> uses optimization level slightly lower than -O1.
>
>> In that case, a tiny change on some often-used macro or function can
>> make a big difference.
>
> But I see no significant difference in my unoptimized builds of both
> branches.

Doesn't -O0 mean unoptimized?  But Gregory Heytings said that -O0
suffers the same performance hit as -Og in emacs-27 but not im master,
which your timings seem to contradict.  What am I missing?

Steve Berman