On Thu, 2016-11-24 at 22:41 +0100, Michael Kerrisk (man-pages) wrote: > Suppose that there are two autogroups competing for the same > CPU. The first group contains ten CPU-bound processes from a > kernel build started with make -j10. The other contains a sin‐ > gle CPU-bound process: a video player. The effect of auto‐ > grouping is that the two groups will each receive half of the > CPU cycles. That is, the video player will receive 50% of the > CPU cycles, rather just 9% of the cycles, which would likely > lead to degraded video playback. Or to put things another way: > an autogroup that contains a large number of CPU-bound pro‐ > cesses does not end up overwhelming the CPU at the expense of > the other jobs on the system. I'd say something more wishy-washy here, like cycles are distributed fairly across groups and leave it at that, as your detailed example is incorrect due to SMP fairness (which I don't like much because [very unlikely] worst case scenario renders a box sized group incapable of utilizing more that a single CPU total). For example, if a group of NR_CPUS size competes with a singleton, load balancing will try to give the singleton a full CPU of its very own. If groups intersect for whatever reason on say my quad lappy, distribution is 80/20 in favor of the singleton. > ┌─────────────────────────────────────────────────────┐ > │FIXME │ > ├─────────────────────────────────────────────────────┤ > │How do the nice value of a process and the nice │ > │value of an autogroup interact? Which has priority? │ > │ │ > │It *appears* that the autogroup nice value is used │ > │for CPU distribution between task groups, and that │ > │the process nice value has no effect there. (I.e., │ > │suppose two autogroups each contain a CPU-bound │ > │process, with one process having nice==0 and the │ > │other having nice==19. It appears that they each │ > │get 50% of the CPU.) It appears that the process │ > │nice value has effect only with respect to schedul‐ │ > │ing relative to other processes in the *same* auto‐ │ > │group. Is this correct? │ > └─────────────────────────────────────────────────────┘ Yup, entity nice level affects distribution among peer entities. -Mike -- To unsubscribe from this list: send the line "unsubscribe linux-man" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
