diff options
author | Huang Ying <ying.huang@intel.com> | 2022-02-10 13:25:14 +0800 |
---|---|---|
committer | Peter Zijlstra <peterz@infradead.org> | 2022-02-11 23:30:08 +0100 |
commit | 3624ba7b5e2acc02b01301ea5fd3534971eb9896 (patch) | |
tree | 1582433b0680361d724cfc81ba795fe2da31fd84 /Documentation/scheduler/sched-debug.rst | |
parent | e496132ebedd870b67f1f6d2428f9bb9d7ae27fd (diff) |
sched/numa-balancing: Move some document to make it consistent with the code
After commit 8a99b6833c88 ("sched: Move SCHED_DEBUG sysctl to
debugfs"), some NUMA balancing sysctls enclosed with SCHED_DEBUG has
been moved to debugfs. This patch move the document for these
sysctls from
Documentation/admin-guide/sysctl/kernel.rst
to
Documentation/scheduler/sched-debug.rst
to make the document consistent with the code.
Signed-off-by: "Huang, Ying" <ying.huang@intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
Acked-by: Mel Gorman <mgorman@techsingularity.net>
Link: https://lkml.kernel.org/r/20220210052514.3038279-1-ying.huang@intel.com
Diffstat (limited to 'Documentation/scheduler/sched-debug.rst')
-rw-r--r-- | Documentation/scheduler/sched-debug.rst | 54 |
1 files changed, 54 insertions, 0 deletions
diff --git a/Documentation/scheduler/sched-debug.rst b/Documentation/scheduler/sched-debug.rst new file mode 100644 index 000000000000..4d3d24f2a439 --- /dev/null +++ b/Documentation/scheduler/sched-debug.rst @@ -0,0 +1,54 @@ +================= +Scheduler debugfs +================= + +Booting a kernel with CONFIG_SCHED_DEBUG=y will give access to +scheduler specific debug files under /sys/kernel/debug/sched. Some of +those files are described below. + +numa_balancing +============== + +`numa_balancing` directory is used to hold files to control NUMA +balancing feature. 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 `scan_period_min_ms, scan_delay_ms, +scan_period_max_ms, scan_size_mb` files. + + +scan_period_min_ms, scan_delay_ms, scan_period_max_ms, scan_size_mb +------------------------------------------------------------------- + +Automatic NUMA balancing scans tasks address space and unmaps pages to +detect if pages are properly placed or if the data should be migrated to a +memory node local to where the task is running. Every "scan delay" the task +scans the next "scan size" number of pages in its address space. When the +end of the address space is reached the scanner restarts from the beginning. + +In combination, the "scan delay" and "scan size" determine the scan rate. +When "scan delay" decreases, the scan rate increases. The scan delay and +hence the scan rate of every task is adaptive and depends on historical +behaviour. If pages are properly placed then the scan delay increases, +otherwise the scan delay decreases. The "scan size" is not adaptive but +the higher the "scan size", the higher the scan rate. + +Higher scan rates incur higher system overhead as page faults must be +trapped and potentially data must be migrated. However, the higher the scan +rate, the more quickly a tasks memory is migrated to a local node if the +workload pattern changes and minimises performance impact due to remote +memory accesses. These files control the thresholds for scan delays and +the number of pages scanned. + +``scan_period_min_ms`` is the minimum time in milliseconds to scan a +tasks virtual memory. It effectively controls the maximum scanning +rate for each task. + +``scan_delay_ms`` is the starting "scan delay" used for a task when it +initially forks. + +``scan_period_max_ms`` is the maximum time in milliseconds to scan a +tasks virtual memory. It effectively controls the minimum scanning +rate for each task. + +``scan_size_mb`` is how many megabytes worth of pages are scanned for +a given scan. |