Performance testing Tool Introduction-linux system command line

This article describes the performance testing of Linux comes with commands, detailing the use of these Linux-brought tools.

First, uptime

The results of the uptime command include how long the server has been running, how many logged-in users, and the overall evaluation of server performance (load average). The load average values are recorded for the last 1 minutes, 5 minutes, and 15 minute intervals, and load average is not a percentage, but the number of processes waiting to be executed in the queue. If the process requires CPU time to be blocked (meaning that the CPU does not have time to handle it), the load average value will increase. On the other hand, if each process can get access to the CPU immediately, this value will be reduced.

The best value for load average is 1, which means that each process can be processed by the CPU at once, and, of course, the lower will not be a problem, only a waste of a portion of the resources. But this value is also different between different systems, such as a single CPU workstation, load average 1 or 2 is acceptable, and in a multi-CPU system This value should be divided by the number of physical CPUs, assuming that the number of CPUs is 4, and load average 8 or 10, The result was at 2多.

You can use uptime to determine whether a performance issue occurs on the server or on the network. For example, if a network application is running at an unsatisfactory performance, run uptime to check if the system load is higher, if not the problem is more likely to occur on your network.

Second, top

The top command shows the actual CPU usage, which by default shows the CPU-intensive task information on the server and refreshes every 5 seconds. You can categorize them in a number of ways, including PID, time, and memory usage.

The following is an introduction to the output values:

Reference

PID: Process identification

User name of the process owner

PRI: Priority of the process

Ni:nice level

VIRT: Amount of memory consumed by the process (code + data + stack)

RES; The amount of physical memory used by the process

SHR; The number of shared memory for this process and other processes

S: Status of the process: s= hibernation, r= running state, t= stop state, d= interrupt sleep state, z= zombie State

%CPU: Shared CPU usage

%MEM; shared physical memory

Time: How long the process consumes CPU

Command: To start a task (including parameters)

Cpu (s): 0.3% US
Percentage of CPU occupied by user space
1.0% Sy
Percentage of CPU consumed by kernel space
0.0% ni
CPU percentage of processes that have changed priority in user process space
98.7% ID
Percentage of idle CPU
0.0% WA
Percentage of CPU time waiting for input and output
0.0% hi
0.0% St

Process priority and nice level

The process priority is a parameter that determines the process is prioritized by the CPU, and the kernel adjusts the value as needed. The nice value is a restriction on priority. The value of the process priority cannot be less than the nice value. (The lower the Nice value the higher the priority)

Process priority cannot be changed manually, but only by changing the nice value to indirectly adjust the process priority level. If a process is running too slowly, you can allocate more CPU resources to it by specifying a lower nice value. Of course, this means that some other processes will be allocated less CPU resources and run slower. Linux supports a nice value with a range of 19 (low priority) to 20 (high priority), and the default value is 0. If you need to change the nice value of a process to a negative number (high priority), you must log on to the root user using the SU command. Here are some examples of commands to adjust nice values.

Start program xyz with nice value-5

#nice –n-5 XYZ

Change the nice value of a program that is already running

#renice level PID

Change the nice value of the process with PID 2500 to 10

#renice 10 2500

Zombie Process

When a process is finished, it usually takes some time to complete all tasks (such as closing open files) before it ends, and in a very short time, the status of this process is zombie state. After the process has completed all the shutdown tasks, it submits the information it closed to the parent process. In some cases, a zombie process cannot shut itself down, when the process state is Z (zombie). You cannot use the KILL command to kill a zombie process because it is already marked as "dead". If you can't get rid of a zombie process, you can kill its parent process, and the zombie process disappears. However, if the parent process is the INIT process, you cannot kill the init process because INIT is an important system process, in which case you can only get rid of the zombie process by restarting the server at once. You also have to analyze why applications can cause zombies.

Third, Iostat

Iostat is part of the Sysstat package. Iostat shows the average CPU time since the system was booted (similar to uptime), which also shows the use of the disk subsystem, IOSTAT can be used to monitor CPU utilization and disk utilization.

CPU utilization is divided into four parts:

Reference

%user:user level (application) CPU usage

%nice: CPU Usage for the user level with nice priority

%sys:system level (kernel) CPU usage

%idle: Idle CPU resource condition

The disk occupancy rate has the following sections:

Reference

Device: Block device name

TPS: The number of devices per second that the device transmits (I/O requests per second). Multiple individual I/O requests can be composed of one transport operation, because a transfer operation can be of different capacity.

BLK_READ/S, BLK_WRTN/S: The number of blocks that the device reads and writes per second. The block may be of different capacity.

Blk_read, Blk_wrtn: The total number of block devices that have been read and written since the system started.

The size of the block

The block may be of different capacity. The size of the block is generally 1024, 2048, 4048byte. Available through TUNE2FS or DUMPE2FS:

Reference

linux-nvk0:/#tune2fs-L/dev/sda1|grep ' Block size '

Block size:4096

linux-nvk0:/#dumpe2fs-H/dev/sda1|grep ' Block size '

DUMPE2FS 1.38 (30-jun-2005)

Block size:4096

Iv. Vmstat

The Vmstat command provides monitoring of information such as processes, memory, page I/O blocks, and CPUs, Vmstat can display the average or sampled values of the test results, and the sampling mode can provide a monitoring result of different frequencies over a sampling period.

Note: In the sampling mode, you need to consider the possible errors in data collection, and set the sampling frequency to a lower value to minimize the effect of the error.

Here's a look at what each column means

Reference

process (procs)

R: Number of processes waiting for run time

B: Process in non-disruptive sleep state

W: Processes that are swapped out but can still be run, this value is calculated

Memory

SWPD: Number of virtual memory

Free: The number of idle memory

Buff: The amount of memory used as a buffer

Swap

Si: Quantity exchanged from hard disk

So: The number of swapped to the hard drive

· Io

BI: Number of blocks output to a single block device

Bo: Number of blocks accepted from a single block device

system

In: Number of interrupts per second, including clock

CS: Number of contextswitches that occur per second

CPU (percent of the total CPU run time)

US: Time for non-kernel code to run (user time, including nice time)

SY: Kernel code run time (System time)

ID: Idle time, in the kernel version prior to Linux 2.5.41, this value includes I/O wait time;

WA: Time to wait for I/O operation, this value is 0 in the kernel version prior to Linux 2.5.41

The Vmstat command provides a number of additional parameters, and some of the most useful parameters are listed below:

Reference

• M: Showing memory utilization of the kernel

A: Display memory page information, including active and inactive memory pages

• N: Displays the header line, which is useful when using sampling mode and outputting command results to a file. For example, Root#vmstat–n 2 10 displays 10 output results at 2-second frequency

• Vmstat provides statistics on I/O results when using the-p {partition}

V, PS and Pstree

The PS and Pstree commands are the most common basic commands for system analysis, and the PS command provides a list of the processes that are running, depending on the parameters attached to the command. For example, the ps–a command lists all processes and their corresponding process IDs (PID), and the PID of the process must be understood before using some other tool, such as Pmap or Renice.

On a system running Java applications, the output of the Ps–a command can easily exceed the display of the screen, which makes it difficult to get complete information for all processes. At this point, you can use the Pstree command to display all process information in a tree structure and to integrate the child process information. The Pstree command is useful for analyzing the source of a process.

Vi.. Sar

The SAR program is also part of the Sysstat installation package. The SAR command is used to collect, report, and save information about the system. The SAR command consists of three applications: SAR, using and displaying data, SA1 and SA2, for collecting and storing data. By default, automatic collection and analysis is added to the crontab:

Reference

[Email protected] ~]# Cat/etc/cron.d/sysstat

# Run System activityaccounting tool every minutes

*/10 * * * * ROOT/USR/LIB/SA/SA1 1 1

# Generate a daily summary of processaccounting at 23:53

* * * root/usr/lib/sa/sa2-a

The data generated by the SAR command is saved in the/var/log/sa/directory, the data is saved according to the time, and the corresponding performance data can be queried according to the time.

You can also use the SAR to get a real-time execution result from the command line, which can include CPU utilization, memory pages, network I/O, and so on. The following command indicates a 5-time interval of 3 seconds in SAR execution:

VII. Free

The free command displays all memory usage for the system, including idle memory, used memory, and swap memory space. The free command display also includes information about the caches and buffers used by the kernel.

When using the free command, it is necessary to remember the memory structure of Linux and the management methods of virtual memory, such as the limit of the amount of idle memory, and the use of swap space does not mark the occurrence of a memory bottleneck.

Parameters useful for the free command:

Reference

-b,-k,-m and-G respectively according to bytes, kilobytes, megabytes, gigabytes display results.

-l difference shows low and high memory

-c {count} shows the number of free outputs

Eight, Pmap

The PMAP command shows the amount of memory used by one or more processes, and you can use this tool to determine which process on the server is consuming too much memory to cause a memory bottleneck.

Nine, Strace

Strace intercepts and records the system invocation information of the process, and also includes the command signals that the process accepts. This is a useful diagnostic and debugging tool that can be used by system administrators to solve program problems by Strace.

command format, you need to specify the process ID that needs to be monitored. This is used more for developers.

Strace-p <pid>

Ten, Mpstat

The Mpstat command is also part of the Sysstat package. The Mpstat command is used to monitor the situation of each available CPU in a multi-CPU system. The Mpstat command shows the operation of each CPU or all CPUs, as well as the use of parameters to monitor sampling results of a certain frequency, as in the case of the Vmstat command.