git: kernel - Refactor scheduler weightings part 1/2.
dillon at crater.dragonflybsd.org
Sun May 26 09:50:21 PDT 2019
Author: Matthew Dillon <dillon at apollo.backplane.com>
Date: Sun May 26 09:37:51 2019 -0700
kernel - Refactor scheduler weightings part 1/2.
* Refactor the scheduler's weightings and fix a few issues that
have cropped up due to breaking previous tunings. This gets
our pgbench results back to normal.
* There will probably be a follow-up commit with a bit more
tuning work, particular with regards to resetting the
td_wakefromcpu field which we currently do not do at all.
* Increase weight1 (keep thread on current CPU) slightly,
implement weight4, and re-tune the algorithm.
* Break-out the IPC pairing control fields into two new
sysctls, kern.usched_dfly.ipc_smt and kern.usched_dfly.ipc_same,
with the default set to -1 (auto).
ipc_smt Tries to schedule IPC pairings onto sibling
hyperthreads to avoid cache mastership changes
when the load is greater than (ncpus / 2).
ipc_same Tries to schedule IPC pairings onto the same
logical cpu to avoid both cache mastership changes
AND IPIs when the load is greater than (ncpus).
* Keep in mind that the scheduler cannot perfectly predict program
behavior. In particular, these IPC pairings can work better or worse
depending on the mix between local cpu use within each process,
verses the amount of data being transfered between them. By default
we try to localize IPC pairings to nearby cores but we do not try
to schedule them to sibling hyperthreads unless the load is high
enough for it to make sense.
* The main IPC weighting is weight2, whereas the fairness metric is
weight4. Generally speaking, weight4 should be somewhat smaller
than weight2 but still high enough to ensure that available CPUs
in the system are reasonably well utilized. Also note that the
fairness metric (weight4) is based on priority-weighted load.
Summary of changes:
sys/kern/kern_synch.c | 9 +-
sys/kern/usched_dfly.c | 262 +++++++++++++++++++++++++++++++++++++++----------
2 files changed, 216 insertions(+), 55 deletions(-)
DragonFly BSD source repository
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