Hello Juri, On 05/13/2014 05:52 PM, Juri Lelli wrote: > Hello, > > On Tue, 13 May 2014 17:00:57 +0200 > "Michael Kerrisk (man-pages)" <mtk.manpages@xxxxxxxxx> wrote: > >> Hello Peter et al. >> >> Here is the section of the sched(7) page that describes SCHED_DEADLINE, >> as rendered text, with the (entire) raw page source attached. Please >> carefully review. >> >> Cheers, >> >> Michael [...] >> The following diagram clarifies these terms: >> >> arrival/wakeup absolute deadline >> | start time | >> | | | >> v v v >> -----x--------xooooooooooooooooo-------x--------x--- >> |<- comp. time ->| >> |<------- relative deadline ----->| >> |<-------------- period ------------------>| >> >> When setting a SCHED_DEADLINE policy for a thread using >> sched_setattr(2), one can specify three parameters: Runtime, >> Deadline, and Period. These parameters do not necessarily >> correspond to the aforementioned terms: usual practice is to >> set Runtime to something bigger than the average computation >> time (or worst-case execution time for hard real-time tasks), >> Deadline to the relative deadline, and Period to the period >> of the task. Thus, for SCHED_DEADLINE scheduling, we have: >> >> arrival/wakeup absolute deadline >> | start time | >> | | | >> v v v >> -----x--------xooooooooooooooooo-------x--------x--- >> |<-- Runtime --->| > > |<-- Runtime --->| > > I originally drew this slightly bigger than comp. time above because we > usually don't want tasks to be throttled in the average case. It's just > a rule of thumb. Ahh -- yes, I see now that I messed this up when I tweaked the ASCII art. Thanks for catching that. Fixed now. >> |<----------- Deadline ---------->| >> |<-------------- Period ------------------>| >> >> The three deadline-scheduling parameters correspond to the >> sched_runtime, sched_deadline, and sched_period fields of the >> sched_attr structure; see sched_setattr(2). These fields >> express value in nanoseconds. If sched_period is specified >> as 0, then it is made the same as sched_deadline. >> >> The kernel requires that: >> >> sched_runtime <= sched_deadline <= sched_period >> >> In addition, under the current implementation, all of the >> parameter values must be at least 1024 (i.e., just over one >> microsecond, which is the resolution of the implementation). > > And below 2^63, as per the last bug fix we discussed. Fixed. Cheers, Michael -- Michael Kerrisk Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/ Linux/UNIX System Programming Training: http://man7.org/training/ -- To unsubscribe from this list: send the line "unsubscribe linux-api" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
