Linux Performance Observability Tools

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agenda

a brief discussion of 6 facets of Linux performance:

  1. observalility
  2. Methodologies
  3. benchmarking
  4. profiling
  5. tracing
  6. tuning

observability tools

  • Tools showcase common metrics
    • lenrning linux tools is useful even if you never use them:
      the same metrics are in GUIs
  • we usually use these metrics via:
    • netflix atlas: cloud-wide monitoring
    • netflix vector: instance analysis
  • Linux has many tools
    • plus many extra kernel sourcse of data that lack tools,are harder to use ,and are practically undocumented

uptime

  • one way to print load averages:
  • a measure of resource demand: CPUs + disk
    • other OSes only show CPUs: easier to interpret
  • exponentially-damped moving averages
  • time constants of 1,5,and 15 minutes
    • historic trend without the line graph
  • Load > # of CPUs,may mean CPU saturation
    • Don’t spent more than 5 seconds studying these

top (or htop)

  • system and per-process interval summary:
  • %CPU is summed across all CPUs
  • Can miss short-lives processes(atop won’t)
  • Can consume noticeable CPU to read/proc

vmstat

  • Virtual memory statistics and more:
  • USAGE:vmstat [interval[count]]
  • First output line has some summary since boot values
    • Should be all;partial is confusing
  • High level CPU summary
    • “r” is runnable tasks

iostat

  • Block I/O (disk)stats.1st output is since boot.
  • very useful set of stats

free

  • Main memory usage:
  • buffers: block device I/O cache
  • cached: virtua; page cache

strace

  • System call tracer:
  • Eg, -ttt:time (us) since epoch;-T:syscall time(s)
  • Translates syscall arges
    • very helpful for solving system usage issues
  • Currently has massive overhead(ptrace based)
    • can slow the target by > 100x.Use extreme caution.

tcpdump

  • sniff network packets for post analysis:
  • study packet sequences with timestamps(us)
  • CPU overhead optimized (socket ring buffers),but can still be significant.use caution.

netstat

  • various network protocol statistics using -s:
  • a multi-tool:
    • i:interface stats
    • r:route table
      default:list conns
  • netstat -p:shows process details!
  • Per-second interval with -c

slabtop

  • Kernel slab allocator memory usage

pcstat

  • show page cache residency
  • Uses the mincore(2)syscall.Useful for database performance analysis.

perf_events

  • Provides the “perf” command
  • in Linux source code:tools/perf
    • Usually pkg added by linux-tools-common.etc.
  • Multi-tool with many capabilities
    • CPU profiling
    • PMC profiling
    • Static & dynamic tracing
  • Covered later in Profiling & Tracing

Methodologies

anti-Methodologies

  • The lack of a deliberate methodology…
  • Street Light Anti-Method:
    1. Pick observability tools that are
      • Familiar
      • Found on the Internet
      • Found at random
    2. Run tools
    3. Look for obvious issues
  • Drunk Man Anti-Method:
    • Tune things at random until the problem goes away

在Linux世界，进程不能直接访问硬件设备，当进程需要访问硬件设备(比如读取磁盘文件，接收网络数据等等)时，必须由用户态模式切换至内核态模式，通 过系统调用访问硬件设备。strace可以跟踪到一个进程产生的系统调用,包括参数，返回值，执行消耗的时间。

ss

ss -l 显示本地打开的所有端口
ss -pl 显示每个进程具体打开的socket
ss -t -a 显示所有tcp socket
ss -u -a 显示所有的UDP Socekt
ss -o state established ‘( dport = :smtp or sport = :smtp )’ 显示所有已建立的SMTP连接
ss -o state established ‘( dport = :http or sport = :http )’ 显示所有已建立的HTTP连接
ss -x src /tmp/.X11-unix/* 找出所有连接X服务器的进程
ss -s 列出当前socket详细信息:

strace

-c 统计每一系统调用的所执行的时间,次数和出错的次数等.
-d 输出strace关于标准错误的调试信息.
-f 跟踪由fork调用所产生的子进程.
-ff 如果提供-o filename,则所有进程的跟踪结果输出到相应的filename.pid中,pid是各进程的进程号.
-F 尝试跟踪vfork调用.在-f时,vfork不被跟踪.
-h 输出简要的帮助信息.
-i 输出系统调用的入口指针.
-q 禁止输出关于脱离的消息.
-r 打印出相对时间关于,,每一个系统调用.
-t 在输出中的每一行前加上时间信息.
-tt 在输出中的每一行前加上时间信息,微秒级.
-ttt 微秒级输出,以秒了表示时间.
-T 显示每一调用所耗的时间.
-v 输出所有的系统调用.一些调用关于环境变量,状态,输入输出等调用由于使用频繁,默认不输出.
-V 输出strace的版本信息.
-x 以十六进制形式输出非标准字符串
-xx 所有字符串以十六进制形式输出.
-a column
设置返回值的输出位置.默认 为40.
-e expr
指定一个表达式,用来控制如何跟踪.格式如下:
[qualifier=][!]value1[,value2]…
qualifier只能是 trace,abbrev,verbose,raw,signal,read,write其中之一.value是用来限定的符号或数字.默认的 qualifier是 trace.感叹号是否定符号.例如:
-eopen等价于 -e trace=open,表示只跟踪open调用.而-etrace!=open表示跟踪除了open以外的其他调用.有两个特殊的符号 all 和 none.
注意有些shell使用!来执行历史记录里的命令,所以要使用\.
-e trace=set
只跟踪指定的系统 调用.例如:-e trace=open,close,rean,write表示只跟踪这四个系统调用.默认的为set=all.
-e trace=file
只跟踪有关文件操作的系统调用.
-e trace=process
只跟踪有关进程控制的系统调用.
-e trace=network
跟踪与网络有关的所有系统调用.
-e strace=signal
跟踪所有与系统信号有关的 系统调用
-e trace=ipc
跟踪所有与进程通讯有关的系统调用
-e abbrev=set
设定 strace输出的系统调用的结果集.-v 等与 abbrev=none.默认为abbrev=all.
-e raw=set
将指 定的系统调用的参数以十六进制显示.
-e signal=set
指定跟踪的系统信号.默认为all.如 signal=!SIGIO(或者signal=!io),表示不跟踪SIGIO信号.
-e read=set
输出从指定文件中读出 的数据.例如:
-e read=3,5
-e write=set
输出写入到指定文件中的数据.
-o filename
将strace的输出写入文件filename
-p pid
跟踪指定的进程pid.
-s strsize
指定输出的字符串的最大长度.默认为32.文件名一直全部输出.
-u username
以username 的UID和GID执行被跟踪的命令