1 ================= 2 Scheduler debugfs 3 ================= 4 5 Booting a kernel with CONFIG_SCHED_DEBUG=y will give access to 6 scheduler specific debug files under /sys/kernel/debug/sched. Some of 7 those files are described below. 8 9 numa_balancing 10 ============== 11 12 `numa_balancing` directory is used to hold files to control NUMA 13 balancing feature. If the system overhead from the feature is too 14 high then the rate the kernel samples for NUMA hinting faults may be 15 controlled by the `scan_period_min_ms, scan_delay_ms, 16 scan_period_max_ms, scan_size_mb` files. 17 18 19 scan_period_min_ms, scan_delay_ms, scan_period_max_ms, scan_size_mb 20 ------------------------------------------------------------------- 21 22 Automatic NUMA balancing scans tasks address space and unmaps pages to 23 detect if pages are properly placed or if the data should be migrated to a 24 memory node local to where the task is running. Every "scan delay" the task 25 scans the next "scan size" number of pages in its address space. When the 26 end of the address space is reached the scanner restarts from the beginning. 27 28 In combination, the "scan delay" and "scan size" determine the scan rate. 29 When "scan delay" decreases, the scan rate increases. The scan delay and 30 hence the scan rate of every task is adaptive and depends on historical 31 behaviour. If pages are properly placed then the scan delay increases, 32 otherwise the scan delay decreases. The "scan size" is not adaptive but 33 the higher the "scan size", the higher the scan rate. 34 35 Higher scan rates incur higher system overhead as page faults must be 36 trapped and potentially data must be migrated. However, the higher the scan 37 rate, the more quickly a tasks memory is migrated to a local node if the 38 workload pattern changes and minimises performance impact due to remote 39 memory accesses. These files control the thresholds for scan delays and 40 the number of pages scanned. 41 42 ``scan_period_min_ms`` is the minimum time in milliseconds to scan a 43 tasks virtual memory. It effectively controls the maximum scanning 44 rate for each task. 45 46 ``scan_delay_ms`` is the starting "scan delay" used for a task when it 47 initially forks. 48 49 ``scan_period_max_ms`` is the maximum time in milliseconds to scan a 50 tasks virtual memory. It effectively controls the minimum scanning 51 rate for each task. 52 53 ``scan_size_mb`` is how many megabytes worth of pages are scanned for 54 a given scan.
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