5/27/2023 0 Comments Linux cpu stats![]() This CPU time math gets quite complicated, so let's look at some diagrams to clarify things. CPU time is determined by dividing the cgroup's CPUShares by the total number of defined CPUShares on the system. Once the system has mounted the cpu cgroup controller, you can use the file cpu.shares to define the number of shares allocated to the cgroup. m option gives this data and it can be used per -processor reporting option too. This helps in calculating power being used by CPU. Here sar shows you processor clock frequency at given instance of time. ![]() The CPUShares value provides tasks in a cgroup with a relative amount of CPU time. Another small stats regarding processor is power stats. This means that you could have multiple schedulers on a single system, depending on how your disks are configured. It is also worth noting that a scheduler can be chosen per block device. These schedulers can be changed, of course, and you should investigate your workload and pick the scheduler that best suits your task(s). This plays an important role in tuning your system. With that in mind, RHEL tends to use cfq for SATA-based drives and deadline for all other cases by default. Read operations take precedence over write batches by default. Operations are completed based on time spent in the queue, and the kernel will always try to process requests before their maximum amount of time has elapsed. ![]() There is one queue for reads and one for writes. Deadline: Attempts to provide a guaranteed latency for requests and is particularly suitable when read operations occur more often than write operations.Completely Fair Queuing (CFQ): Emphasizes I/O coming from real-time processes and uses historical data to decide whether an application will issue more I/O requests in the near future.Most of the Red Hat family of products (Fedora, CentOS, and RHEL) use either deadline or cfq as the default schedulers. Therefore, some of my points could apply to other distributions, as well. However, in my quick look at the few Ubuntu boxes in my lab, I noticed similarities with the I/O scheduler. I'm going to take a very narrow focus on Red Hat Enterprise Linux (RHEL) for this section. ![]()
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