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linux_wiki:high_system_load [2015/10/07 22:47] billdozor [Traffic/Bridge analogy] |
linux_wiki:high_system_load [2019/05/25 23:50] (current) |
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| **Checklist** | **Checklist** | ||
| - | * Distro: Enterprise Linux 6.x | + | * Distro(s): Enterprise Linux 6 |
| ---- | ---- | ||
| + | |||
| ====== Understanding System Load ====== | ====== Understanding System Load ====== | ||
| Line 26: | Line 27: | ||
| * Load of 1.00 means the bridge is at capacity. No more cars(processes) at this very second can get CPU time without waiting. | * Load of 1.00 means the bridge is at capacity. No more cars(processes) at this very second can get CPU time without waiting. | ||
| * Load over 1.00 means there is a backup. | * Load over 1.00 means there is a backup. | ||
| - | * 2.00 => there are "two lanes" worth of cars(processes) waiting for CPU time. | + | * 2.00 => there are "two lanes" worth of cars(processes). One lane is being processed, another lane is waiting for CPU time. |
| **Multi-CPU/ | **Multi-CPU/ | ||
| Line 33: | Line 34: | ||
| * 2 CPU/Cores = 100% is load 2.00 | * 2 CPU/Cores = 100% is load 2.00 | ||
| * 4 CPU/Cores = 100% is load 4.00 | * 4 CPU/Cores = 100% is load 4.00 | ||
| - | * Example: From the analogy above, each CPU Core can handle | + | * Example: From the analogy above, each CPU Core can actively process |
| ===== Calculate Overall CPU Load ===== | ===== Calculate Overall CPU Load ===== | ||
| - | * Get number of CPUs | + | * Get number of CPUs< |
| - | * <code bash> | + | OR |
| + | nproc</ | ||
| * Load Average / NumProccessors = decimal % load | * Load Average / NumProccessors = decimal % load | ||
| * Example: LoadAvg(1.5) / 2 Processors = 0.75 or 75% system load on a dual core system. | * Example: LoadAvg(1.5) / 2 Processors = 0.75 or 75% system load on a dual core system. | ||
| Line 92: | Line 94: | ||
| ---- | ---- | ||
| - | ==== High CPU ==== | + | ===== High CPU ===== |
| Clues that you should investigate high CPU usage: | Clues that you should investigate high CPU usage: | ||
| Line 109: | Line 111: | ||
| ---- | ---- | ||
| - | ==== High Memory Use ==== | + | ===== High Memory Use ===== |
| + | |||
| + | Notes on Linux memory management | ||
| + | * Linux uses free memory in RAM as a buffer cache to speed up application performance. | ||
| + | * When memory is needed, the buffer cache shrinks to allow other applications to use it. | ||
| + | * **Actual free memory = Memory Free + Buffers + Cached** | ||
| Clues that you should investigate high memory usage: | Clues that you should investigate high memory usage: | ||
| Line 131: | Line 138: | ||
| ---- | ---- | ||
| - | ==== Disk I/O ==== | + | ===== Disk I/O ===== |
| + | |||
| + | * I/O wait (wa) is the percentage of time a CPU is waiting on disk. | ||
| + | * If I/O wait % is > (1/# CPU cores), then the CPUs are spending a lot of time waiting on disk. | ||
| + | * Easiest ways to improve disk I/O | ||
| + | * Give the system more memory | ||
| + | * Tune the application to use more in memory caches than disk | ||
| Clues that you should investigate high Disk I/O: | Clues that you should investigate high Disk I/O: | ||
| Line 137: | Line 150: | ||
| * High CPU " | * High CPU " | ||
| + | \\ | ||
| **iostat** - View I/O stats with extended statistics, every 3 seconds | **iostat** - View I/O stats with extended statistics, every 3 seconds | ||
| <code bash> | <code bash> | ||
| Line 143: | Line 157: | ||
| * " | * " | ||
| + | \\ | ||
| **iotop** - Live disk I/O similar to top | **iotop** - Live disk I/O similar to top | ||
| <code bash> | <code bash> | ||
| Line 148: | Line 163: | ||
| </ | </ | ||
| + | \\ | ||
| **lsof** - If a particular device is discovered, another option for further details is to list open files for that mount point. | **lsof** - If a particular device is discovered, another option for further details is to list open files for that mount point. | ||
| * Device discovered via iostat | * Device discovered via iostat | ||