On Wed, 2021-09-15 at 19:49 +0300, Ville Syrjälä wrote: > On Wed, Sep 15, 2021 at 06:57:19PM +0300, Ville Syrjälä wrote: > > On Wed, Sep 15, 2021 at 04:48:49PM +0300, Ville Syrjälä wrote: > > > On Mon, Sep 13, 2021 at 10:54:14PM +0000, Souza, Jose wrote: > > > > On Thu, 2021-09-09 at 23:28 +0300, Ville Syrjälä wrote: > > > > > On Thu, Sep 09, 2021 at 08:23:20PM +0000, Souza, Jose wrote: > > > > > > On Thu, 2021-09-09 at 23:20 +0300, Ville Syrjälä wrote: > > > > > > > On Thu, Sep 09, 2021 at 12:49:16PM -0700, José Roberto de Souza wrote: > > > > > > > > By now all the userspace applications should have migrated to atomic > > > > > > > > or at least be calling DRM_IOCTL_MODE_DIRTYFB. > > > > > > > > > > > > > > > > With that we can kill frontbuffer rendering support in i915 for > > > > > > > > modern platforms. > > > > > > > > > > > > > > > > So here converting legacy APIs into atomic commits so it can be > > > > > > > > properly handled by driver i915. > > > > > > > > > > > > > > > > Several IGT tests will fail with this changes, because some tests > > > > > > > > were stressing those frontbuffer rendering scenarios that no userspace > > > > > > > > should be using by now, fixes to IGT should be sent soon. > > > > > > > > > > > > > > > > > > > > > > I just gave this a try here and it's unusable. glxgears went from > > > > > > > 9000 to 120 fps (was expecting 60fps tbh, not sure why I get > > > > > > > double), everything lags like mad, if I drag a window around > > > > > > > glxgears/other windows stop updating entirely, etc. NAK > > > > > > > > > > > > Can you share your setup? What GPU? Desktop environment? Mesa version? resolutions of sinks? > > > > > > Will try it in my end. > > > > > > > > > > Doesn't really matter as long as you don't have a compositor making a > > > > > mess of things. This machine is a cfl running mate w/ compositor off, > > > > > and some 1920x1200 display. > > > > > > > > > > > > > Making drm_atomic_helper_dirtyfb() do a non-blocking atomic commit makes user experience pretty similar to the one with compositing enabled: > > > > drm_atomic_commit() + compositor off: https://youtu.be/NBt6smXs99U > > > > drm_atomic_nonblocking_commit() + compositor off: https://youtu.be/QiMhkeGX_L8 > > > > drm_atomic_nonblocking_commit() + compositor on: https://youtu.be/KdpJyJ5k6sQ > > > > > > > > > > > > I do not completly agree with the comment in drm_atomic_helper_dirtyfb() about why it uses a blocking implementation. > > > > With frontbuffer rendering the registers are programmed but the content could only show up for user a whole frame later. > > > > > > > > Perhaps if this solutions is accetable we could have a non-blocking version of drm_atomic_helper_dirtyfb() so the drivers current using it don't have > > > > their behavior changed. > > > > > > Non-blocking update would make sense to me, whereas a blocking > > > update makes no sense given how this is used by actual userspace. > > > > Actually neither maybe makes total sense since userspace probably > > isn't expecting -EBUSY from dirtyfb. So we might end up with stale > > junk on the screen if no further updates come in after an -EBUSY. 1000 dirtyfb calls will only have a different dirty areas, when executing a dirtyfb atomic commit we could append all the pending dirty areas into this atomic commit and remove all the pending dirtyfb atomic commits. I doubt that userspace will be able to fill WQ_MAX_ACTIVE dirtyfb calls in one single frame. > > One option would be to teach userspace to retry after an -EBUSY, but > without a completion event from dirtyfb it's going to be hard to know > when to retry. > > > > > The current frontbuffer stuff works much more like a mailbox style > > update so we don't lose stuff and neither do we block. > > I suppose the obvious solution would be to teach kms to do proper > mailbox updates. But that is not entirely trivial. One way to simplify > the proposal a bit is to limit it to pure pageflips, which would > suffice for dirtyfb as well obviously. That way watermarks and other > potentially tricky stuff wouldn't change. > > But actually figuring out the proper commit sequence for this might > take some doing. The way I think it should work is that we just let > each commit through without blocking on the previous one. A later > commit may simply overwrite the hardware registers before the > values written by the previous commit get latched. The vblank evasion > stuff would make it perfectly safe. > > The hardest thing there is probably figuring out how to handle all > the pre/post_plane_update() stuff properly since we can't know > ahead of time whether the flip gets latched or not, and so we can't > really use the old state during state computation to make any > decisions affecting our future behaviour. But given that async flips > are more or less working today might mean that I'm worried about nothing. > Either that or async flips are in fact broken in some funny ways I've not > yet realized... > > The other problem for actual mailbox page flips is completion events/out > fences. The current out fence I think is not really suitable for cases > where a flip ends up getting overwritten by a later one, and thus the > fb rotation no longer follows the normal fifo order. But of we don't > expose actual mailbox page flips through the uapi then we could avoid > worrying about this stuff initially. >
