On Mon, May 20, 2013 at 5:48 PM, Juri Lelli <juri.le...@gmail.com> wrote: > On 05/20/2013 12:27 PM, Ola Liljedahl wrote: >> >> Predictable response times for specific threads. In the use cases I >> am aware of, these threads would probably belong to the same process >> and run core-affine on a specific core where as few as possible other >> (kernel and user) threads and interrupts etc would also run. A number >> of cores would follow this real-time model while other cores >> preferably would keep the original Linux scheduling and >> characteristics (to avoid introducing unexpected behaviour). >> >> What benefits does SCHED_DEADLINE give in addition to stuff in >> PREEMPT_RT? >> > > Predictable response times are what SCHED_DEADLINE is about. > > With SCHED_DEADLINE you can provide temporal guarantees up to 100% CPU > utilization that are not possibile with default real-time policies > (e.g. SCHED_FIFO/RR). This comes from the fact that SCHED_DEADLINE > achieves strong temporal isolation between tasks. You can reserve a > fraction of CPU time to your activities and be assured that no one else > can interfere with them. And this is critical also in a low loaded > system, if you want to be really safe against unexpected interferences. > > Basically, with SCHED_DEADLINE you can make a feasibility study (no > deadline will be missed) of the system under development beforehand, > and be sure, at run-time, that the timing requirements will be met > under any circumstance. You can't do the same using only stuff already > in PREEMPT_RT. > > Best, > > - Juri
Over and above what Juri explained, you probably want to keep an eye on the Adaptive Tickless work[1]. It allows cpu isolation so that only the designated task will run on the 'tickless' cores - no scheduling, no interrupts or timers. PMWG has been tracking for its cpu isolation properties and Kevin Hilman landed 32-bit ARM support for the underlying context tracking in 3.10 [2]. Regards, Amit [1] https://wiki.linaro.org/WorkingGroups/PowerManagement/Doc/AdaptiveTickless [2] 64-bit support still WIP _______________________________________________ linaro-dev mailing list linaro-dev@lists.linaro.org http://lists.linaro.org/mailman/listinfo/linaro-dev
