On Fri, Dec 15, 2023 at 01:15:16PM +0200, Ville Syrjälä wrote: > On Wed, Dec 13, 2023 at 05:29:12PM +0200, Ville Syrjälä wrote: > > On Wed, Dec 13, 2023 at 05:15:06PM +0200, Ville Syrjälä wrote: > > > On Wed, Dec 13, 2023 at 01:28:15PM +0200, Lisovskiy, Stanislav wrote: > > > > On Wed, Dec 13, 2023 at 12:25:19PM +0200, Ville Syrjala wrote: > > > > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > > > > > > > This reverts commit cfeff354f70bb1d0deb0279506e3f7989bc16e28. > > > > > > > > > > A core design consideration with legacy cursor updates is that the > > > > > cursor must not touch any other plane, even if we were to force it > > > > > to take the slow path. That is the real reason why the cursor uses > > > > > a fixed ddb allocation, not because bspec says so. > > > > > > > > > > Treating cursors as any other plane during ddb allocation > > > > > violates that, which means we can now pull other planes into > > > > > fully unsynced legacy cursor mailbox commits. That is > > > > > definitely not something we've ever considered when designing > > > > > the rest of the code. The noarm+arm register write split in > > > > > particular makes that dangerous as previous updates can get > > > > > disarmed pretty much at any random time, and not necessarily > > > > > in an order that is actually safe (eg. against ddb overlaps). > > > > > > > > > > So if we were to do this then: > > > > > - someone needs to expend the appropriate amount of brain > > > > > cells thinking through all the tricky details > > > > > > > > So question is how can we avoid pulling other planes to the commit?.. > > > > > > By preallocating the ddb, as we do already. > > > > I guess one thing we could consider is allcating the cursor ddb > > based on the cursors real size (as opposed to always allocating for > > 256x256 cursor), and not doing a mailbox update when changing size. > > But as we learn in https://gitlab.freedesktop.org/drm/intel/-/issues/7687: > > - current userspace always uses 256x256 until the PLANE_SIZE_HINTS > > stuff (or something similar) lands, so there is no point > > - it would lead to worse power consumption with smaller cursors > > as there isn't enough extra ddb. The fact that we currently > > allocate the minimum for 256x256 means smallers cursor sizes > > are more efficient. Some tests I did also indicated that the > > current code does not give optimal values even if we let it > > fully calculate the extra ddb like in the reverted commit here. > > We really need someone to take a proper look at how to tune > > the ddb allocation for optimal power consumption... > > Oh, and another random idea I keep having occasionally would > be to by default assume that legacy cursor uapi wouldn't be > used, and then massage stuff sufficiently when the first use > appears to make it work well from that point onwards. That > way we could try to be a bit more optimal with ddb/other > stuff for userspace that never uses the legacy cursor uapi. > But haven't really thought through the details on this one. Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@xxxxxxxxx> > > -- > Ville Syrjälä > Intel
