From: Mel Gorman <mgorman@techsingularity.net>
To: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@redhat.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
Li Aubrey <aubrey.li@linux.intel.com>,
Qais Yousef <qais.yousef@arm.com>,
LKML <linux-kernel@vger.kernel.org>,
Mel Gorman <mgorman@techsingularity.net>
Subject: [PATCH v3 0/5] Scan for an idle sibling in a single pass
Date: Tue, 19 Jan 2021 11:22:06 +0000 [thread overview]
Message-ID: <20210119112211.3196-1-mgorman@techsingularity.net> (raw)
Changelog since v2
o Remove unnecessary parameters
o Update nr during scan only when scanning for cpus
Changlog since v1
o Move extern declaration to header for coding style
o Remove unnecessary parameter from __select_idle_cpu
This series of 5 patches reposts three patches from Peter entitled
"select_idle_sibling() wreckage". It only scans the runqueues in a single
pass when searching for an idle sibling.
Two patches from Peter were dropped. The first patch altered how scan
depth was calculated. Scan depth deletion is a random number generator
with two major limitations. The avg_idle time is based on the time
between a CPU going idle and being woken up clamped approximately by
2*sysctl_sched_migration_cost. This is difficult to compare in a sensible
fashion to avg_scan_cost. The second issue is that only the avg_scan_cost
of scan failures is recorded and it does not decay. This requires deeper
surgery that would justify a patch on its own although Peter notes that
https://lkml.kernel.org/r/20180530143105.977759909@infradead.org is
potentially useful for an alternative avg_idle metric.
The second patch dropped converted the idle core scan throttling
mechanism to SIS_PROP. While this would unify the throttling of core
and CPU scanning, it was not free of regressions and has_idle_cores is
a fairly effective throttling mechanism with the caveat that it can have
a lot of false positives for workloads like hackbench.
Peter's series tried to solve three problems at once, this subset addresses
one problem. As with anything select_idle_sibling, it's a mix of wins and
losses but won more than it lost across a range of workloads and machines.
kernel/sched/core.c | 18 +++--
kernel/sched/fair.c | 161 ++++++++++++++++++++--------------------
kernel/sched/features.h | 1 -
kernel/sched/sched.h | 2 +
4 files changed, 95 insertions(+), 87 deletions(-)
--
2.26.2
next reply other threads:[~2021-01-19 11:39 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-19 11:22 Mel Gorman [this message]
2021-01-19 11:22 ` [PATCH 1/5] sched/fair: Remove SIS_AVG_CPU Mel Gorman
2021-01-19 11:22 ` [PATCH 2/5] sched/fair: Move avg_scan_cost calculations under SIS_PROP Mel Gorman
2021-01-19 11:22 ` [PATCH 3/5] sched/fair: Make select_idle_cpu() proportional to cores Mel Gorman
2021-01-19 11:22 ` [PATCH 4/5] sched/fair: Remove select_idle_smt() Mel Gorman
2021-01-19 11:22 ` [PATCH 5/5] sched/fair: Merge select_idle_core/cpu() Mel Gorman
2021-01-20 8:30 ` Gautham R Shenoy
2021-01-20 9:12 ` Mel Gorman
2021-01-20 9:21 ` Vincent Guittot
2021-01-20 9:54 ` Mel Gorman
2021-01-20 9:58 ` Vincent Guittot
2021-01-20 13:55 ` Gautham R Shenoy
2021-01-19 11:33 ` [PATCH v3 0/5] Scan for an idle sibling in a single pass Vincent Guittot
2021-01-19 12:02 ` Mel Gorman
2021-01-22 9:30 ` Vincent Guittot
2021-01-22 10:14 ` Mel Gorman
2021-01-22 13:22 ` Vincent Guittot
2021-01-25 4:29 ` Li, Aubrey
2021-01-25 9:04 ` Mel Gorman
2021-01-25 11:37 ` Li, Aubrey
2021-01-25 11:46 ` Mel Gorman
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