GNU bug report logs - #28695
26.0.60; Rendering lag spikes caused by double-buffering on Linux

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From: Eli Zaretskii <eliz <at> gnu.org>
To: Dmitry Gutov <dgutov <at> yandex.ru>
Cc: 28695 <at> debbugs.gnu.org, bryan <at> bryan.sh, npostavs <at> users.sourceforge.net
Subject: bug#28695: 26.0.60; Rendering lag spikes caused by double-buffering on Linux
Date: Mon, 09 Oct 2017 17:03:37 +0300

> Cc: npostavs <at> users.sourceforge.net, bryan <at> bryan.sh, 28695 <at> debbugs.gnu.org
> From: Dmitry Gutov <dgutov <at> yandex.ru>
> Date: Mon, 9 Oct 2017 16:53:18 +0300
> 
> On 10/7/17 11:14 AM, Eli Zaretskii wrote:
> 
> > Can some of you use a tool like perf to see whether the time taken by
> > XdbeSwapBuffers (called from xterm.c:show_back_buffer) indeed grows
> > significantly when going from the 2K class of resolutions to the 4K
> > class?  And if it isn't XdbeSwapBuffers, then what takes most of the
> > time which causes that "stutter"?
> 
> With some pointers on how to use perf, I'd be happy to do that

I think this page (which you probably already know about) is a good
starting point:

  http://www.brendangregg.com/perf.html

> (or even without, if you're willing to wait).

There's no rush, so please take your time.

> But I'm not seeing a qualitative difference between a 4K fullscreen 
> Emacs, a half-screen Emacs, or even Emacs with window resized further 
> down: there are still minor stutters here. So I'm probably not the best 
> person for this experiment.

Well, you saw a difference between a 4K display and a 2K display,
didn't you?  All we need is to compare 2 situations and see where's
the extra time spent.

Maybe Bryan could also try the profile, as he reported a significant
difference.

Thanks.

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