On Tue, 2010-08-31 at 23:39 +0200, Henrik Rydberg wrote: > On 08/31/2010 11:27 PM, Chase Douglas wrote: > > > On Tue, 2010-08-31 at 23:18 +0200, Henrik Rydberg wrote: > >> On 08/31/2010 11:16 PM, Chase Douglas wrote: > >> > >>> On Tue, 2010-08-31 at 23:06 +0200, Henrik Rydberg wrote: > >>>> On 08/31/2010 10:58 PM, Chase Douglas wrote: > >>>> > >>>>> On Tue, 2010-08-31 at 22:34 +0200, Henrik Rydberg wrote: > >>>>>> On 08/31/2010 08:41 PM, Chase Douglas wrote: > >>>>>> > >>>>>>> The Magic Mouse device is very precise. No driver filtering of input > >>>>>>> data needs to be performed. > >>>>>>> > >>>>>>> Signed-off-by: Chase Douglas <chase.douglas@xxxxxxxxxxxxx> > >>>>>>> Acked-by: Michael Poole <mdpoole@xxxxxxxxxxx> > >>>>>>> --- > >>>>>> > >>>>>> > >>>>>> I am still not sure this is a good idea. Bandwidth from MT devices is a big > >>>>>> deal. A statement roughly how much data comes out of mtdev (which does the > >>>>>> filtering for type A devices) before and after this change would be reassuring. > >>>>> > >>>>> As it is right now, hid-magicmouse doesn't support MT slots. I think all > >>>>> the fuzz code ends up comparing in the MT case is between one touch and > >>>>> another touch, not between one touch's current location and its previous > >>>>> location. If I'm correct, then it means a fuzz > 0 is incorrect for > >>>>> non-slotted MT devices. > >>>>> > >>>>> In fact, the code in drivers/input/input.c around line 194 looks like it > >>>>> discards defuzzing in this case, so one could say this patch is making > >>>>> things more correct :). > >>>> > >>>> > >>>> For type A devices, the filtering is performed in userspace, in mtdev, in the > >>>> same manner as it would have been performed in the kernel in the MT slot case. > >>>> Therefore, knowing the amount of messages coming out of mtdev is a direct > >>>> measurement of the effect of filtering. > >>> > >>> Yes, but we're only interested in the kernel driver when reviewing this > >>> patch. Leaving the fuzz in as it is has no effect right now on ABS_MT_* > >>> axes. On the other axes, such as the touch orientation, it's probably > >>> more harmful than good. > >> > >> > >> "We" are interested in knowing if this patch makes any sense, given that > >> filtering is in actuality performed in userspace, and thus modifying this code > >> changes the stream rate into userspace applications, thank you. > > > > Because in-kernel defuzzing is turned off for ABS_MT_* axes on > > non-slotted MT devices, there will be no change in the number of events > > sent to the userspace due to this patch. > > > > Maybe I'm missing something more fundamental. In which case, I'll need > > more details to get it through my dense skull :). > > > All events passes through to mtdev, yes, but mtdev filters a considerable amount > of events from passing through to X drivers like evdev. Thus, the fuzz values > reported in the kernel driver impacts the performance in userspace, even if > filtering is not done in the kernel. My disconnect was that I didn't understand that the fuzz value in the kernel is exported to userspace. I thought the defuzzing in mtdev was independent of the defuzzing in the kernel. Basically, I don't feel I have the time to do the analysis you want right now. If you really want, I can just remove this change. -- Chase -- To unsubscribe from this list: send the line "unsubscribe linux-input" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
