| From: |
| Ricardo Neri <ricardo.neri-calderon-AT-linux.intel.com> |
| To: |
| "Peter Zijlstra (Intel)" <peterz-AT-infradead.org>, Juri Lelli <juri.lelli-AT-redhat.com>, Vincent Guittot <vincent.guittot-AT-linaro.org> |
| Subject: |
| [PATCH 0/4] sched/fair: Avoid unnecessary migrations within SMT domains |
| Date: |
| Thu, 25 Aug 2022 15:55:25 -0700 |
| Message-ID: |
| <20220825225529.26465-1-ricardo.neri-calderon@linux.intel.com> |
| Cc: |
| Ricardo Neri <ricardo.neri-AT-intel.com>, "Ravi V. Shankar" <ravi.v.shankar-AT-intel.com>, Ben Segall <bsegall-AT-google.com>, Daniel Bristot de Oliveira <bristot-AT-redhat.com>, Dietmar Eggemann <dietmar.eggemann-AT-arm.com>, Len Brown <len.brown-AT-intel.com>, Mel Gorman <mgorman-AT-suse.de>, "Rafael J. Wysocki" <rafael.j.wysocki-AT-intel.com>, Srinivas Pandruvada <srinivas.pandruvada-AT-linux.intel.com>, Steven Rostedt <rostedt-AT-goodmis.org>, Tim Chen <tim.c.chen-AT-linux.intel.com>, Valentin Schneider <vschneid-AT-redhat.com>, x86-AT-kernel.org, linux-kernel-AT-vger.kernel.org, Ricardo Neri <ricardo.neri-calderon-AT-linux.intel.com> |
| Archive-link: |
| Article |
Intel processors that support Intel Turbo Boost Max 3.0 use asym_packing
to assign higher priorities to CPUs with higher maximum frequencies. It
artificially assigns, however, a lower priority to the higher-numbered
SMT siblings to ensure that they are used last.
This results in unnecessary task migrations within the SMT domains.
On processors with a mixture of higher-frequency SMT cores and lower-
frequency non-SMT cores (such as Intel hybrid processors), a lower-
priority CPU pulls tasks from the higher-priority cores if more than one
SMT sibling is busy.
Do not use different priorities for each SMT sibling. Instead, tweak the
asym_packing load balancer to recognize SMT cores with more than one
busy sibling and let lower-priority CPUs pull tasks.
Removing these artificial priorities avoids superfluous migrations and
lets lower-priority cores inspect all SMT siblings for the busiest queue.
Thanks and BR,
Ricardo
Ricardo Neri (4):
sched/fair: Simplify asym_packing logic for SMT sched groups
sched/fair: Do not disqualify either runqueues of SMT sched groups
sched/fair: Let lower-priority CPUs do active balancing
x86/sched: Avoid unnecessary migrations within SMT domains
arch/x86/kernel/itmt.c | 23 +++++-----------------
kernel/sched/fair.c | 44 ++++++++++++++++++++----------------------
2 files changed, 26 insertions(+), 41 deletions(-)
--
2.25.1
