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sched/numa: Favour moving tasks towards the preferred node

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This patch favours moving tasks towards NUMA node that recorded a higher
number of NUMA faults during active load balancing.  Ideally this is
self-reinforcing as the longer the task runs on that node, the more faults
it should incur causing task_numa_placement to keep the task running on that
node. In reality a big weakness is that the nodes CPUs can be overloaded
and it would be more efficient to queue tasks on an idle node and migrate
to the new node. This would require additional smarts in the balancer so
for now the balancer will simply prefer to place the task on the preferred
node for a PTE scans which is controlled by the numa_balancing_settle_count
sysctl. Once the settle_count number of scans has complete the schedule
is free to place the task on an alternative node if the load is imbalanced.

[[email protected]: Fixed statistics]
Signed-off-by: Mel Gorman <[email protected]>
Reviewed-by: Rik van Riel <[email protected]>
Cc: Andrea Arcangeli <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Srikar Dronamraju <[email protected]>
[ Tunable and use higher faults instead of preferred. ]
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
This commit is contained in:
Mel Gorman 2013-10-07 11:29:00 +01:00 • committed by Ingo Molnar
commit 3a7053b322
6 changed files with 83 additions and 6 deletions
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8
Documentation/sysctl/kernel.txt
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@ -375,7 +375,8 @@ feature should be disabled. Otherwise, if the system overhead from the
feature is too high then the rate the kernel samples for NUMA hinting
faults may be controlled by the numa_balancing_scan_period_min_ms,
numa_balancing_scan_delay_ms, numa_balancing_scan_period_reset,
numa_balancing_scan_period_max_ms and numa_balancing_scan_size_mb sysctls.
numa_balancing_scan_period_max_ms, numa_balancing_scan_size_mb and
numa_balancing_settle_count sysctls.
==============================================================
@ -420,6 +421,11 @@ scanned for a given scan.
numa_balancing_scan_period_reset is a blunt instrument that controls how
often a tasks scan delay is reset to detect sudden changes in task behaviour.
numa_balancing_settle_count is how many scan periods must complete before
the schedule balancer stops pushing the task towards a preferred node. This
gives the scheduler a chance to place the task on an alternative node if the
preferred node is overloaded.
==============================================================
osrelease, ostype & version: