On 7/4/06, Pavel Machek <pavel at ucw.cz> wrote: > Just use input infrastructure and be done with that? You can do > parking from userspace. Will moving the hdapsd userspace daemon from sysfs polling to the input infrastructure cause a noticable latency increase compared to polling sysfs? This functionality is highly time-critical. Also, there's a small issue with polling frequency. hdapsd needs a fairly high frequency (say, 50Hz) to gather statistics and keep response latency low, whereas the hdaps driver's internal polling (routing to the input infrastructure) is currently done at only 20Hz. We'll need to increase the latter, thereby slightly increasing system load when hdaps isn't running. In terms of magnitude, an hdaps readout takes ~70usec on average and (very rarely) up to ~1msec. This is with the tp_smapi [1] patches to hdaps, which add the checks and retries needed to ensure the readout is valid. BTW, can the driver tell when nothing is accessing its input device, and avoid polling in that case? Shem [1] http://thinkwiki.org/wiki/tp_smapi
