[Wayland-bugs] [Bug 86815] XWayland [weston 1.6.0] takes all CPU and is very slow on eee-pc

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=86815

            Bug ID: 86815
           Summary: XWayland [weston 1.6.0] takes all CPU and is very slow
                    on eee-pc
           Product: Wayland
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: XWayland
          Assignee: wayland-bugs at lists.freedesktop.org
          Reporter: mildred-bug.freedesktop at mildred.fr
        QA Contact: xorg-team at lists.x.org

Running weston with the xwayland.so module on current ArchLinux (weston
1.6.0-1) cause on some computers XWayland to take all the CPU available (100%
of one CPU core out of the two cores available on the system), and is very
slow. X11 windows are shown but unusable.

This happens on a eee-pc 1005PE. Processor is dual core intel atom N450 with
integrated intel graphics. On another computer running the same distro (and
same package versions) but with an i7 processor, I have no problems, and
XWayland CPU usage is more than correct.

I noticed the following pattern:

- running an X11 application cause XWayland to consume the most CPU
- after some time focusing on a wayland native application, XWayland stops
eating CPU
- if focusing on the X11 window again (or simply hovering the mouse), CPU
consumption rise again to 100%
- wayland surfaces continue to be responsive (that's nice actually)
- I notice glitches on X11 window decorations (the title bar disappear, then
reappear). That may be unrelated though.

Looking at the Xwayland process using strace, I found a unusual number of
SIGALRM signals being catched by Xwayland. I have the following sequence
repeated many many many times:

--- SIGALRM {si_signo=SIGALRM, si_code=SI_KERNEL} ---
rt_sigreturn() = (number that varies a lot, 0, 1 and higher integers)

There are some ioctl in the mix and very few other system calls

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