LFS201 Lab 15.1 Comparing I/O Schedulers.

Hi, I'm not sure of the workflow for getting the lab.iosched.sh script to run for this lab.
Im using Ubuntu 20.4 and the command to use was;
$ sudo ./lab_iosched.sh [# reads/writes (NMAX)] [file size in MB (NMEGS)]
How do I get the file into a place where Linux knows where to find it and run it?
Comments
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Probably chmod +x lab_iosched.sh will do.
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Note: we worked this in the Office Hours session. Need to do just 'sudo ./lab_iosched.sh' for starting. doing 'less lab_iosched.sh' will provide more information about the parameters.
Regards,
Luis.0 -
Yes, you will have to make it executable probably if you downloaded in place. If you got from the "SOLUTIONS" tar ball it already is executable. Your results will depend on distro and kernel. For example I just ran it on Ubuntu 20.04 and the only IO schedulers were "mq-deadline" and "none". On RHEL 8 you have also "bfq" which is actually the default, at least for a vanilla kernel.
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Mark: You mentioned during the office hour that you didn't manage to set sudo permissions for your default user. I sent you a private message with examples for /etc/sudoers and /etc/group configurations.
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hi @luisviveropena , I fininshed this lab, but I dont understand how to compare the results. Could you please hellp me to interpret the results of running this script? I understand that it is comparing four different I/O scheduling strategies, but the results mean what?. For example, what does this means:
testing IOSCHED = mq-deadline [mq-deadline] kyber bfq none 0.517 0.010 0.752
The full output from the script on my system is like this:
[javier@fedora Downloads]$ sudo ./lab_iosched.sh 16 300 Doing: 16 parallel read/writes on: 300 MB size files creating as needed random input files doing timings of parallel reads REAL USER SYS testing IOSCHED = mq-deadline [mq-deadline] kyber bfq none 0.517 0.010 0.752 testing IOSCHED = kyber mq-deadline [kyber] bfq none 0.522 0.008 0.645 testing IOSCHED = bfq mq-deadline kyber [bfq] none 0.522 0.008 1.062 testing IOSCHED = none [none] mq-deadline kyber bfq 0.527 0.011 1.072 doing timings of parallel writes REAL USER SYS testing IOSCHED = none [none] mq-deadline kyber bfq 0.102 0.056 0.217 testing IOSCHED = mq-deadline [mq-deadline] kyber bfq none 0.091 0.033 0.216 testing IOSCHED = kyber mq-deadline [kyber] bfq none 0.094 0.043 0.220 testing IOSCHED = bfq mq-deadline kyber [bfq] none 0.102 0.035 0.140
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Reading the lab_iosched.sh script that produces the output would tell you what the numbers are. For example the output for the write test is produced by the line:
time do_write_test
the three numbers are: wallclock (real) time, user (process) time, and system (kernel) time, in seconds. There are actually these three headings in the output. In hyour results there are very few differences, as can be explained by choice of hardware, linux kernel etc, and if you are on a virtual machine you may have trouble seeing the differences as it is a fake environment. On my real workstation I get:
ROOT@c9:/tmp/TEMP>../lab_iosched.sh Doing: 8 parallel read/writes on: 100 MB size files creating as needed random input files 100+0 records in 100+0 records out 104857600 bytes (105 MB, 100 MiB) copied, 0.304284 s, 345 MB/s doing timings of parallel reads REAL USER SYS testing IOSCHED = mq-deadline [mq-deadline] kyber bfq none 0.158 0.009 0.627 testing IOSCHED = kyber mq-deadline [kyber] bfq none 0.155 0.005 0.637 testing IOSCHED = bfq mq-deadline kyber [bfq] none 0.164 0.007 0.645 testing IOSCHED = none [none] mq-deadline kyber bfq 0.156 0.005 0.689 doing timings of parallel writes REAL USER SYS testing IOSCHED = none [none] mq-deadline kyber bfq 24.404 0.011 1.052 testing IOSCHED = mq-deadline [mq-deadline] kyber bfq none 25.426 0.013 1.116 testing IOSCHED = kyber mq-deadline [kyber] bfq none 25.788 0.011 0.958 testing IOSCHED = bfq mq-deadline kyber [bfq] none 23.774 0.010 0.891 Once again not much difference. Modern hardware such as SSD drives has rendered this kind of issue mostly moot except on certain kinds of situations and the deadline scheduler is almost always the best choice. It is here partly just so you understand that the kernel has to make decsions about what to read and write and when and in what order
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