Messages in this thread | | | Date | Fri, 27 Aug 2010 17:20:52 +0200 (CEST) | From | Thomas Gleixner <> | Subject | Re: [RFC PATCH 00/11] sched: CFS low-latency features |
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On Fri, 27 Aug 2010, Mathieu Desnoyers wrote: > * Paul E. McKenney (paulmck@linux.vnet.ibm.com) wrote: > > Why couldn't the timer_create() call record the start time, and then > > compute the sleeps from that time? So if timer_create() executed at > > time t=100 and the period is 5, upon awakening and completing the first > > invocation of the function in question, the thread does a sleep calculated > > to wake at t=110. > > Let's focus on the userspace thread execution, right between the samping of the > current time and the call to sleep: > > Thread A > current_time = read current time(); > sleep(period_end - current_time); > > If the thread is preempted between these two operations, then we end up sleeping > for longer than what is needed. This kind of imprecision will add up over time, > so that after e.g. one day, instead of having the expected number of timer > executions, we'll have less than that. This kind of accumulated drift is an > unwanted side-effect of using delays in lieue of real periodic timers.
Nonsense, that's why we provide clock_nanosleep(ABSTIME)
Thanks,
tglx
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