On Mon, 2014-08-04 at 13:52 -0700, bseg...@google.com wrote: > Jason Low <jason.l...@hp.com> writes: > > > 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 > > > > Signed-off-by: Jason Low <jason.l...@hp.com> > Reviewed-by: Ben Segall <bseg...@google.com> > > That said, it might be better to remove force_update for this function, > or make it just reduce the minimum to /64 or something. If the test is > easy to run it would be good to see what it's like just removing the > force_update param for this function to see if it's worth worrying > about or if the zero case catches ~all the perf gain.
Sure, I can test that out too. I did notice when running another AIM7 workload that !zero was the more common case, so this has the potential to further reduce contention. > Paul, your thoughts? -- 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/
