Hi Pekka,

Thanks for the information, I will talk to my mentor Daniel and try to find
out
what I can do about this.

Cheers,
Zhao Junwang

On Fri, Jul 17, 2015 at 2:08 PM, Pekka Paalanen <ppaalanen@gmail.com> wrote:

> On Thu, 16 Jul 2015 20:20:39 +0800
> John Hunter <zhjwpku@gmail.com> wrote:
>
> > From: Zhao Junwang <zhjwpku@gmail.com>
> >
> > This supports the asynchronous commits, required for page-flipping
> > Since it's virtual hw it's ok to commit async stuff right away, we
> > never have to wait for vblank.
>
> Hi,
>
> in theory, yes. This is what a patch to bochs implemented not too long
> ago, so AFAIK you are only replicating the existing behaviour.
>
> However, if userspace doing an async commit (or sync, I suppose) does
> not incur any waits in the kernel in e.g. sending the page flip event,
> then flip driven programs (e.g. a Wayland compositor, say, Weston)
> will be running its rendering loop as a busy-loop, because the kernel
> does not throttle it to the (virtual) display refresh rate.
>
> This will cause maximal CPU usage and poor user experience as
> everything else needs to fight for CPU time and event dispatch to get
> through, like input.
>
> I would hope someone could do a follow-up to implement a refresh cycle
> emulation based on a clock. Userspace expects page flips to happen at
> most at refresh rate when asking for vblank-synced flips. It's only
> natural for userspace to drive its rendering loop based on the vblank
> cycle.
>
>
> Thanks,
> pq
>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> > Signed-off-by: Zhao Junwang <zhjwpku@gmail.com>
> > ---
> >  drivers/gpu/drm/bochs/bochs_mm.c |    9 ++++++++-
> >  1 file changed, 8 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/bochs/bochs_mm.c
> b/drivers/gpu/drm/bochs/bochs_mm.c
> > index c1d819c..37ac2ca 100644
> > --- a/drivers/gpu/drm/bochs/bochs_mm.c
> > +++ b/drivers/gpu/drm/bochs/bochs_mm.c
> > @@ -545,8 +545,15 @@ bochs_user_framebuffer_create(struct drm_device
> *dev,
> >       return &bochs_fb->base;
> >  }
> >
> > +static int bochs_atomic_commit(struct drm_device *dev,
> > +                          struct drm_atomic_state *a,
> > +                          bool async)
> > +{
> > +     return drm_atomic_helper_commit(dev, a, false);
> > +}
> > +
> >  const struct drm_mode_config_funcs bochs_mode_funcs = {
> >       .fb_create = bochs_user_framebuffer_create,
> >       .atomic_check = drm_atomic_helper_check,
> > -     .atomic_commit = drm_atomic_helper_commit,
> > +     .atomic_commit = bochs_atomic_commit,
> >  };
>
>


-- 
Best regards
Junwang Zhao
Microprocessor Research and Develop Center
Department of Computer Science &Technology
Peking University
Beijing, 100871, PRC