On Friday 23 October 2015 20:32:50 Pingbo Wen wrote:
do_gettimeofday(&tv);tv.tv_usec += USEC_PER_SEC * (tv.tv_sec - mlc->instart.tv_sec);tv.tv_usec -= mlc->instart.tv_usec;if (tv.tv_usec >= mlc->intimeout) goto sched;tv.tv_usec = (mlc->intimeout - tv.tv_usec) * HZ / USEC_PER_SEC;if (!tv.tv_usec) goto sched;mod_timer(&hil_mlcs_kicker, jiffies + tv.tv_usec);
if (tmp.tv64 >= (mlc->intimeout * NSEC_PER_USEC))goto sched;tmp.tv64 = mlc->intimeout * NSEC_PER_USEC - tmp.tv64;if (tmp.tv64 < NSEC_PER_USEC)goto sched;mod_timer(&hil_mlcs_kicker,jiffies + nsecs_to_jiffies(tmp.tv64)); break;If I read this right, the code is executed one for each input event such as a keypress or mouse movement. In the latter case, doing nsecs_to_jiffies() here is actually a bit expensive, and I stil think it can be avoided by just using jiffies.
For the (tmp.tv64 < NSEC_PER_USEC) part, did you just do that because I said this, or did you actually prove that it is required? I'm still confused about what the driver is trying to achieve here.
More explanation here:) the judgement here is to prevent mod_timer with zero delta. I can not make sure whether the module have nanosecond precise, so just keep same.
Ok, I guess I was misreading the original code. What it actually does is to check the remaining time in jiffies, not in microseconds, so the algorithm is:
if (already expired) schedule tasklet else { convert to jiffies if (expired just now) schedule tasklet else schedule tasklet from timer }
So the entire code is meant to guarantee that the tasklet is getting scheduled, and the first two cases are just an optimization to avoid going through the timer. I checked the code for mod_timer to verify that mod_timer with an argument in the past will just cause the handler to be called at the next tick, so we don't really need the middle case, and the logic becomes really simple if you use jiffies instead of ktime_t.
Arnd