On Mon, Aug 04, 2014 at 01:28:38PM -0700, Jason Low wrote: > When running workloads on 2+ socket systems, based on perf profiles, the > update_cfs_rq_blocked_load function constantly shows up as taking up a > noticeable % of run time. This is especially apparent on an 8 socket > machine. For example, when running the AIM7 custom workload, we see: > > 4.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load > > Much of the contention is in __update_cfs_rq_tg_load_contrib when we > update the tg load contribution stats. However, it turns out that in many > cases, they don't need to be updated and "tg_contrib" is 0. > > This patch adds a check in __update_cfs_rq_tg_load_contrib to skip updating > tg load contribution stats when nothing needs to be updated. This reduces the > cacheline contention that would be unnecessary. In the above case, with the > patch, perf reports the total time spent in this function went down by more > than a factor of 3x: > > 1.18% reaim [kernel.kallsyms] [k] update_cfs_rq_blocked_load >
Supposedly adding something like __cacheline_aligned to task_group::load_avg is also rumoured to help. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
