Linux high IOwait is a common Linux performance issue. Today we will look at what iowait means and what contributes to this problem. Hope this can give you more ideas about high IOwait issue. What is IOwait? IO wait is related to the CPU resource on the server. The iowait column on...
top 命令,我们发现%wa 的值,达到20以上,甚至40以上,此时,我们就要明确,现在CPU 大量消耗在等待IO响应上了。请注意,是在等待IO响应,而不是在等待磁盘完成IO操作. 这两者之间的区别在于,等待IO响应, 可能链路没反应,请求根本没有到达磁盘,也有 可能磁盘损坏,无法响应,高IO wait 不一定代表磁盘很忙。 因此分析这种...
Finding the processes that are causing high I/O 查找引起高I/O wait 对应的进程 iotop # iotop Total DISK READ: 8.00 M/s | Total DISK WRITE: 20.36 M/s TID PRIO USER DISK READ DISK WRITE SWAPIN IO> COMMAND 15758 be/4 root 7.99 M/s 8.01 M/s 0.00 % 61.97 % bonnie++ -n 0 -...
High I/O wait forces the server to handle higher bandwidth to perform other computations while waiting on IO requests. I/O wait is a common metric to analyze system performance. When high I/O wait occurs frequently, it can negatively impact system performance by slowing down the system or ca...
看到app确实在通过系统调用sys_read()读取数据,并且从new_sync_read和blkdev_direct_IO看出进程时进行直接读操作,请求直接从磁盘读,没有通过缓存导致iowait升高。 通过层层分析后,root cause是app内部进行了磁盘的直接I/O。然后定位到具体代码位置进行优化即可。
High iowaits on specific CPU cores The io workload on the CPU cores are not evenly distributed. This is a expected behavior of a Linux kernel. When a CPU encounters a task that requires an I/O operation, it sends a request to an I/O controller. The responsibility of the I/O control...
1. iowait无法升高的问题,是因为案例中stress使用的是 sync() 系统调用,它的作用是刷新缓冲区内存到磁盘中。对于新安装的虚拟机,缓冲区可能比较小,无法产生大的IO压力,这样大部分就都是系统调用的消耗了。所以,你会看到只有系统CPU使用率升高。解决方法是使用stress的下一代stress-ng,它支持更丰富的选项,比如 str...
缺点:如果内存不足会导致系统性能下降,可能会造成磁盘IO洪水,如果断电未写入磁盘的脏页数据可能会丢失。 例如:将页面缓存得大小改为1G # 1. 修改内核参数 ehigh@ubuntu:~$ sudo vim /etc/sysctl.conf vm.dirty_bytes=1073741824 # 将脏页的内存量调整为1G ...
从CPU这行,可以发现CPU的io wait;这里是96.0%。越高就代表CPU用于io wait的资源越多。 2. 找出哪个磁盘正在被写入 上边的top命令从一个整体上说明了I/O wait,但是并没有说明是哪块磁盘影响的,想知道是哪块磁盘引发的问题,可以使用另外一个命令 iostat 命令 ...
iowait can in some cases be an indicator of a limiting factor to transaction throughput whereas in other cases, iowait may be completely meaningless. Some examples here will help to explain this. The first example is one where high iowait is a direct cause ...