I’ve been running a benchmark today on my old test box with conventional hard drives (no raid with BBU) and noticed something unusual in the CPU utilization statistics being reported.

The benchmark was run like this:

sysbench --num-threads=64 --max-requests=0 --max-time=600000 --report-interval=10 --test=oltp --db-driver=mysql --oltp-dist-type=special  --oltp-table-size=1000000   --mysql-user=root --mysql-password=password  run

Which means: create 64 threads and hammer the database with queries as quickly as possible. As the test was run on the localhost I would expect the benchmark to completely saturate the system – being either using CPU or being blocked on IO nature of this benchmark so it does not spend a lot on database locks, especially as this system has just 2 cores.

Looking at VMSTAT however I noticed this:

[root@smt1 mysql]# vmstat 10
procs -----------memory---------- ---swap-- -----io---- …

A beautiful picture is sometimes better than words :

With standard HDDs (here in RAID 10), the innodb_io_capacity variable may have non expected effects.

You can see on this picture the result of a test on one of my server with only the replication thread activated. The value of the innodb_io_capacity variable was the single modification during the period.

So, don’t touch this parameter without a strong reason…
(Of course 30000 was a bit snooty)

[MAJ 2013-01-08] : I know 30k is a too high value for innodb_io_capacity, I used this value to make the graphe really eloquent.
Read this excellent post from Chris for more details : http://www.chriscalender.com/?p=201

…

I prefer to say right now, the answer is no !
However, mpstat can provide a minimum service to show essentials information about your CPU usage :

Show usage for all CPU (every 1s) : mpstat 1

Show usage for CPU number 2 (every 1s) : mpstat -P 2 1

It’s possible to retrieve CPU load (user/sys) and IO waits via a simple interface.
And I like the opportunity to focus on a single CPU. It can be a usefull tool for monitoring and scripting.

But there isn’t any information about the run queue processes and this is the bad news here !

So, let me know if you’ve used this tool, all comments are welcome.

…

I prefer to say right now, the answer is no !
However, mpstat can provide a minimum service to show essentials information about your CPU usage :

Show usage for all CPU (every 1s) : mpstat 1

Show usage for CPU number 2 (every 1s) : mpstat -P 2 1

It’s possible to retrieve CPU load (user/sys) and IO waits via a simple interface.
And I like the opportunity to focus on a single CPU. It can be a usefull tool for monitoring and scripting.

But there isn’t any information about the run queue processes and this is the bad news here !

So, let me know if you’ve used this tool, all comments are welcome.

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