Need xcb/xkb help for severe kglobalaccel_x11 issue

[Albert Astals Cid]

El dissabte, 30 de gener de 2021, a les 18:32:32 CET, David Faure va escriure:
> For years, I've noticed that when resuming a laptop from sleep, kglobalaccel and X11 
> use 100% CPU for a few minutes, making everything crawl for a while.

Does this happen on a short sleep too or needs a long sleep?

If happens with a short sleep, i can't reproduce it :/

I just added https://ghostbin.com/paste/Xqgd4 and all i get is https://ghostbin.com/paste/LMa9n after suspending and resuming a few times.

> I finally debugged why: kglobalaccel grabs and ungrabs all global shortcuts many many times in a row.
> 
> KGlobalAccelImpl::nativeEventFilter event->response_type= 85 xkbEvent= 1 calling x11MappingNotify()
> KGlobalAccelImpl::x11MappingNotify Got XMappingNotify event
> KGlobalAccelInterface::ungrabKeys 
> KGlobalAccelInterface::grabKeys 
> KGlobalAccelImpl::nativeEventFilter event->response_type= 85 xkbEvent= 1 calling x11MappingNotify()
> KGlobalAccelImpl::x11MappingNotify Got XMappingNotify event
> KGlobalAccelInterface::ungrabKeys 
> KGlobalAccelInterface::grabKeys 
> and so on, and so on...
> 
> The reason why x11MappingNotify() does ungrabKeys+grabKeys is apparently "Maybe the X modifier map has been changed."
> ... which is not the case at all...
> 
> What's an XCB_XKB_MAP_NOTIFY anyway?  http://manpages.ubuntu.com/manpages/xenial/en/man3/xcb_xkb_map_notify_event_t.3.html
> is very much incomplete...
> 
> Is it event really such an event that we're getting?
> The code says
> 
>     } else if (m_xkb_first_event && responseType == m_xkb_first_event) {
>         const uint8_t xkbEvent = event->pad0;
>         switch (xkbEvent) {
>             case XCB_XKB_MAP_NOTIFY:
>                 qDebug() << "event->response_type=" << event->response_type << "xkbEvent=" << xkbEvent << "calling x11MappingNotify()";
>                 x11MappingNotify();
>                 break;
> 
> What sense does it make that this code is checking pad0, which looks like some padding member? To avoid a downcast to a more specific event type maybe?
> 
> I'm not sure:
> * if we're really getting a stream of XCB_XKB_MAP_NOTIFY events or if this code misunderstands that
> * if so, why is X11 sending such a high number of those
> * why the code reacts the same to XCB_XKB_MAP_NOTIFY and to XCB_MAPPING_NOTIFY, isn't one enough?

Far from an expert, but i think they are two ways (pure XCB or XKB over XCB (which is why it uses pad0 to get out the xkb event from the xcb one)) to notify the same, so I would say it makes sense to handle both.

Cheers,
  Albert

> 
> Without outside help I guess I would just compress those events using a timer, but that would be a "fix without really understanding the code", never good.
> 
> I just noticed https://phabricator.kde.org/D16434 so CC'ing Fabian :)
>                 
>