# CentOS 7
This page describes the Optimization Pack for the component type CentOS 7.
## Metrics
### CPU
| Metric | Unit | Description |
| ------------------ | ------- | ----------------------------------------------------------------------------------------------------------------- |
| cpu\_num | CPUs | The number of CPUs available in the system (physical and logical) |
| cpu\_util | percent | The average CPU utilization % across all the CPUs (i.e., how much time on average the CPUs are busy doing work) |
| cpu\_util\_details | percent | The average CPU utilization % broken down by usage type and cpu number (e.g., cp1 user, cp2 system, cp3 soft-irq) |
| cpu\_load\_avg | tasks | The system load average (i.e., the number of active tasks in the system) |
### Memory
| Metric | Unit | Description |
| ------------------ | -------- | -------------------------------------------------------------------------------------------------------------- |
| mem\_util | percent | The memory utilization % (i.e, the % of memory used) |
| mem\_util\_nocache | percent | The memory utilization % (i.e., the % of memory used) without considering memory reserved for caching purposes |
| mem\_util\_details | percent | The memory utilization % (i.e., the % of memory used) broken down by usage type (e.g., active memory) |
| mem\_used | bytes | The total amount of memory used |
| mem\_used\_nocache | bytes | The total amount of memory used without considering memory reserved for caching purposes |
| mem\_total | bytes | The total amount of installed memory |
| mem\_fault\_minor | faults/s | The number of minor memory faults (i.e., faults that do not cause disk access) per second |
| mem\_fault\_major | faults/s | The number of major memory faults (i.e., faults that cause disk access) per second |
| mem\_fault | faults/s | The number of memory faults (major + minor) |
| mem\_swapins | pages/s | The number of memory pages swapped in per second |
| mem\_swapouts | pages/s | The number of memory pages swapped out per second |
### Network
| Metric | Unit | Description |
| ---------------------------- | --------- | ------------------------------------------------------------------------------------------------------ |
| network\_tcp\_retrans | retrans/s | The number of network TCP retransmissions per second |
| network\_in\_bytes\_details | bytes/s | The number of inbound network packets in bytes per second broken down by network device (e.g., wlp4s0) |
| network\_out\_bytes\_details | bytes/s | The number of outbound network packets in bytes per second broken down by network device (e.g., eth01) |
### Disk
Notice: you can use a `device` custom filter to monitor a specific disk with Prometheus. You can find more information on Prometheus queries and the `%FILTERS%` placeholder here: [Prometheus provider](https://docs.akamas.io/akamas-docs/3.6/integrating/integrating-telemetry-providers/prometheus-provider) and here: [Prometheus provider metrics mapping](https://docs.akamas.io/akamas-docs/3.6/reference/telemetry-metric-mapping/prometheus-metrics-mapping).
| Metric | Unit | Description |
| ----------------------------- | ------- | -------------------------------------------------------------------------------------------------------------------------------------------- |
| disk\_swap\_util | percent | The average space utilization % of swap disks |
| disk\_swap\_used | bytes | The total amount of space used by swap disks |
| disk\_util\_details | percent | The utilization % of disk, i.e how much time a disk is busy doing work broken down by disk (e.g., disk D://) |
| disk\_iops\_writes | ops/s | The average number of IO disk-write operations per second across all disks |
| disk\_iops\_reads | ops/s | The average number of IO disk-read operations per second across all disks |
| disk\_iops | ops/s | The average number of IO disk operations per second across all disks |
| disk\_response\_time\_read | seconds | The average response time of IO read-disk operations |
| disk\_response\_time\_worst | seconds | The average response time of IO disk operations of the slowest disk |
| disk\_response\_time\_write | seconds | The average response time of IO write-disk operations |
| disk\_response\_time\_details | ops/s | The average response time of IO disk operations broken down by disk (e.g., disk /dev/nvme01 ) |
| disk\_iops\_details | ops/s | The number of IO disk-write operations of per second broken down by disk (e.g., disk /dev/nvme01) |
| disk\_io\_inflight\_details | ops | The number of IO disk operations in progress (outstanding) broken down by disk (e.g., disk /dev/nvme01) |
| disk\_write\_bytes | bytes/s | The number of bytes per second written across all disks |
| disk\_read\_bytes | bytes/s | The number of bytes per second read across all disks |
| disk\_read\_write\_bytes | bytes/s | The number of bytes per second read and written across all disks |
| disk\_write\_bytes\_details | bytes/s | The number of bytes per second written from the disks broken down by disk and type of operation (e.g., disk /dev/nvme01 and operation WRITE) |
| disk\_read\_bytes\_details | bytes/s | The number of bytes per second read from the disks broken down by disk and type of operation (e.g., disk /dev/nvme01 and operation READ) |
### Filesystem
| Metric | Unit | Description |
| ---------------- | ------- | ------------------------------------------------------------------------------------------------------------------------------- |
| filesystem\_util | percent | The space utilization % of filesystems broken down by type and device (e.g., filesystem of type overlayfs on device /dev/loop1) |
| filesystem\_used | bytes | The amount of space used on the filesystems broken down by type and device (e.g., filesystem of type zfs on device /dev/nvme01) |
| filesystem\_size | bytes | The size of filesystems broken down by type and device (e.g., filesystem of type ext4 for device /dev/nvme01) |
### Other metrics
| Metric | Unit | Description |
| ------------------- | ---------- | ----------------------------------------------------------------- |
| proc\_blocked | processes | The number of processes blocked (e.g, for IO or swapping reasons) |
| os\_context\_switch | switches/s | The number of context switches per second |
## Parameters
### CPU
| Parameter | Default Value | Domain | Description |
| ----------------------------- | ------------- | -------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| os\_cpuSchedMinGranularity | 2250000 ns | 300000→30000000 ns | Minimal preemption granularity (in nanoseconds) for CPU bound tasks |
| os\_cpuSchedWakeupGranularity | 3000000 ns | 400000→40000000 ns | Scheduler Wakeup Granularity (in nanoseconds) |
| os\_CPUSchedMigrationCost | 500000 ns | 100000→5000000 ns | Amount of time (in nanoseconds) after the last execution that a task is considered to be "cache hot" in migration decisions. A "hot" task is less likely to be migrated to another CPU, so increasing this variable reduces task migrations |
| os\_CPUSchedChildRunsFirst | 0 | 0→1 | A freshly forked child runs before the parent continues execution |
| os\_CPUSchedLatency | 18000000 ns | 2400000→240000000 ns | Targeted preemption latency (in nanoseconds) for CPU bound tasks |
| os\_CPUSchedAutogroupEnabled | 1 | 0→1 | Enables the Linux task auto-grouping feature, where the kernel assigns related tasks to groups and schedules them together on CPUs to achieve higher performance for some workloads |
| os\_CPUSchedNrMigrate | 32 | 3→320 | Scheduler NR Migrate |
### Memory
| Parameter | Default Value | Domain | Description |
| ------------------------------------ | -------------- | ------------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| os\_MemorySwappiness | 1 | 0→100 | Memory Swappiness |
| os\_MemoryVmVfsCachePressure | 100 % | 10→100 % | VFS Cache Pressure |
| os\_MemoryVmMinFree
| 67584 KB | 10240→1024000 KB | Minimum Free Memory |
| os\_MemoryVmDirtyRatio | 20 % | 1→99 % | When the dirty memory pages exceed this percentage of the total memory, processes are forced to write dirty buffers during their time slice instead of continuing to write |
| os\_MemoryVmDirtyBackgroundRatio | 10 % | 1→99 % | When the dirty memory pages exceed this percentage of the total memory, the kernel begins to write them asynchronously in the background |
| os\_MemoryTransparentHugepageEnabled | `always` | `always` `never` | Transparent Hugepage Enablement |
| os\_MemoryTransparentHugepageDefrag | `always` | `always` `never` | Transparent Hugepage Enablement Defrag |
| os\_MemorySwap | `swapon` | `swapon` `swapoff` | Memory Swap |
| os\_MemoryVmDirtyExpire | 3000 centisecs | 300→30000 centisecs | Memory Dirty Expiration Time |
| os\_MemoryVmDirtyWriteback | 500 centisecs | 50→5000 centisecs | Memory Dirty Writeback |
### Network
| Parameter | Default value | Domain | Description |
| ---------------------------------------- | ------------------- | ------------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------- |
| os\_NetworkNetCoreSomaxconn | 128 connections | 12→1200 connections | Network Max Connections |
| os\_NetworkNetCoreNetdevMaxBacklog | 1000 packets | 100→10000 packets | Network Max Backlog |
| os\_NetworkNetIpv4TcpMaxSynBacklog | 1024 packets | 52→15120 packets | Network IPV4 Max Sync Backlog |
| os\_NetworkNetCoreNetdevBudget | 300 packets | 30→3000 packets | Network Budget |
| os\_NetworkNetCoreRmemMax
| 212992 bytes | 21299→2129920 bytes | Maximum network receive buffer size that applications can request |
| os\_NetworkNetCoreWmemMax
| 21299→2129920 bytes | 21299→2129920 bytes | Maximum network transmit buffer size that applications can request |
| os\_NetworkNetIpv4TcpSlowStartAfterIdle | 1 | 0→1 | Network Slow Start After Idle Flag |
| os\_NetworkNetIpv4TcpFinTimeout | 60 | 6 →600 seconds | Network TCP timeout |
| os\_NetworkRfs | 0 | 0→131072 | If enabled increases datacache hitrate by steering kernel processing of packets to the CPU where the application thread consuming the packet is running |
### Storage
| Parameter | Default value | Domain | Description |
| ----------------------------------- | ------------- | ----------------- | ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |
| os\_StorageReadAhead
| 128 KB | 0→1024 KB | Read-ahead speeds up file access by pre-fetching data and loading it into the page cache so that it can be available earlier in memory instead of from disk |
| os\_StorageNrRequests | 1000 packets | 100→10000 packets | Network Max Backlog |
| os\_StorageRqAffinity | 1 | 1→2 | Storage Requests Affinity |
| os\_StorageQueueScheduler | `none` | `none` `kyber` | Storage Queue Scheduler Type |
| os\_StorageNomerges
| 0 | 0→2 | Enables the user to disable the lookup logic involved with IO merging requests in the block layer. By default (0) all merges are enabled. With 1 only simple one-hit merges will be tried. With 2 no merge algorithms will be tried |
| os\_StorageMaxSectorsKb | 128 KB | 32→128 KB | The largest IO size that the OS c |
## Constraints
There are no general constraints among CentOS 7 parameters.