Measure the test taker's knowledge about Linux system performance indicators.

Operating systems are getting more and more attention from computer users. The Linux operating system is also the most famous example in the development of free software and open source code. Before introducing various tuning parameters and performance monitoring tools for Linux systems, we need to discuss some performance indicators for Linux systems. Linux is an open-source operating system, so a large number of available performance monitoring tools. The choice of these tools depends on your personal preferences and requirements for data details. I hope you will learn the Linux System Performance Indicators well.

All performance monitoring tools work according to the same rules, so no matter which monitoring tool you use, you need to understand these parameters. Some important parameters are listed below, so it is useful to understand them effectively.

1) processor Parameters
CPU utilization
This is a simple parameter that intuitively describes the utilization of each CPU. In the xSeries architecture, if the CPU utilization exceeds 80% for a long time, it may be a bottleneck of the processor.

Runable processes
This value describes the process to be executed. In a duration, this value should not exceed 10 times the number of physical CPUs; otherwise, there may be a bottleneck on the CPU.

Blocked
Describes the processes that cannot be executed because they wait for the end of the I/O operation. Blocked may point out that you are facing an I/O bottleneck.

User time
Describes the percentage of processes processed by users, including nice time. If the value of User time is very high, it indicates that the system performance is used in actual work.

System time
Describes the percentage of CPU spending on Kernel operations, including IRQ and software interruptions. If the system time is very high, it indicates that the system may have bottlenecks in network or driver stack. A system usually takes only a small amount of time to process kernel operations.

Idle time
The percentage of idle CPU.

Nice time
This section describes the percentage of CPU spending on re-nicing processes.

Context switch
Number of threads in the system to exchange.

Waiting
CPU spent the total time waiting for I/O operations. Similar to blocked, a system should not spend too much time waiting for I/O operations, otherwise, you should further check whether the I/O subsystem has a bottleneck.

Interrupts
Interrupts values include hard Interrupts and soft Interrupts. Hard Interrupts has more adverse effects on system performance. The high Interrupts value indicates that the system may have a software bottleneck, which may be the kernel or driver. Note that the Interrupts value includes 1000 Interrupts values per second in the modern xServer system due to CPU clock interruption ).

2) memory Parameters
Free memory
Compared with other operating systems, the Linux idle memory value should not be used as an important indicator for Performance Reference, because, as we mentioned earlier, the Linux kernel allocates a large amount of unused memory as the cache of the file system, so this value is usually relatively small.

Swap usage
This value describes the used swap space. Swap usage only indicates the Linux memory management validity. For identifying memory bottlenecks, Swap In/Out is a more meaningful basis, if the value of Swap In/Out remains between 200 and 300 pages per second for a long time, the system may have a memory bottleneck.

Buffer and cache
This value describes the cache allocated to the file system and Block devices. Note that in Red Hat Enterprise Linux 3 and earlier versions, most idle memory will be allocated for Cache Usage. In Versions later than Red Hat Enterprise Linux 4, you can modify page_cache_tuning in/proc/sys/vm to adjust the number of idle memory as cache.

Slabs
Describes the memory space used by the kernel. Note that the page of the kernel cannot be switched to the disk.

Active versus inactive memory
Provides information about the active memory of the system memory. Inactive memory is the space exchanged by the kswapd daemon to the disk.

3) Network Parameters
Packets received and sent
This parameter indicates the number of packets received and sent by a specified Nic.

Bytes encoded Ed and sent
This parameter indicates the number of bytes of data packets received and sent by a specified Nic.

Collisions per second
This value provides the number of network conflicts that occur on the specified Nic. The continuous occurrence of this value indicates a bottleneck in the network architecture, rather than a problem on the server. Conflicts are rare in normal network configurations, unless your network environment is composed of hubs.

Packets dropped
This value indicates the number of data packets dropped by the kernel, probably because of a lack of firewall or network cache.

Overruns
Overruns indicates the number of times the network interface is cached. This parameter should be associated with the packets dropped value to determine whether the bottleneck exists in the network cache or the network queue is too long.

Errors
This value records the number of frames marked as failed. This may be caused by incorrect network configuration or damage to some network cables. Damage to some network cables in a copper port Gigabit Ethernet environment is an important factor affecting performance.

4) block Device Parameters
Iowait
The time the CPU spends waiting for I/O operations. This continuous high value is usually caused by I/O bottlenecks.

Average queue length
The number of I/O requests. Generally, a disk queue value of 2 to 3 is the best condition. A higher value indicates that the system may have an I/O bottleneck.

Average wait
The average time of responding to an I/O operation. Average wait includes the actual I/O operation time and the waiting time in the I/O queue.

Transfers per second
Description of the number of I/O operations per second, including read and write operations ). The combination of Transfers per second value and kBytes per second can help you estimate the average size of the system's transmission blocks, this transfer block size is usually consistent with the Strip size of the disk subsystem to achieve the best performance.

Blocks read/write per second
This value indicates the number of blocks reads and writes per second. In kernel 2.6, blocks is 1024 bytes. In earlier kernel versions, blocks may be of different sizes, from bytes to 4 kb.

Kilobytes per second read/write
The actual data volume of the read/write block device is measured in kb.

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