Subject: Re: bug#28695: 26.0.60; Rendering lag spikes caused by double-buffering on Linux

From: Eli Zaretskii <[email-masked]>
Date: Mon, 09 Oct 2017 17:03:37 +0300

> Cc: [email-masked], [email-masked], [email-masked]
> From: Dmitry Gutov <[email-masked]>
> 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.