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The linux kernel version 0.99.11 (dated 11 July 1993) needed a timing loop (the time is too short and/or needs to be too exact for a non-busy-loop method of waiting), which must be calibrated to the processor speed of the machine. Hence, the kernel measures at boot time how fast a certain kind of busy loop runs on a computer.
The Time Stamp Counter was once a high-resolution, low-overhead way for a program to get CPU timing information. With the advent of multi-core/hyper-threaded CPUs, systems with multiple CPUs, and hibernating operating systems, the TSC cannot be relied upon to provide accurate results — unless great care is taken to correct the possible flaws: rate of tick and whether all cores (processors ...
time (Unix) - can be used to determine the run time of a program, separately counting user time vs. system time, and CPU time vs. clock time. [1] timem (Unix) - can be used to determine the wall-clock time, CPU time, and CPU utilization similar to time (Unix) but supports numerous extensions.
For example, one can interpret a load average of "1.73 0.60 7.98" on a single-CPU system as: During the last minute, the system was overloaded by 73% on average (1.73 runnable processes, so that 0.73 processes had to wait for a turn for a single CPU system on average). During the last 5 minutes, the CPU was idling 40% of the time, on average.
The LINPACK benchmark report appeared first in 1979 as an appendix to the LINPACK user's manual. [4]LINPACK was designed to help users estimate the time required by their systems to solve a problem using the LINPACK package, by extrapolating the performance results obtained by 23 different computers solving a matrix problem of size 100.
The proc filesystem (procfs) is a special filesystem in Unix-like operating systems that presents information about processes and other system information in a hierarchical file-like structure, providing a more convenient and standardized method for dynamically accessing process data held in the kernel than traditional tracing methods or direct access to kernel memory.
The Linux kernel has a subsystem called "cpufreq", tunable by power-scheme and command line, devoted to the control of the operating frequency and voltage of a CPU. Linux runs on Intel, AMD, and other makes of CPU. [13] [14] Newer version Windows 10 and Linux kernel support Intel Speed Shift Technology.
Use of the Linux msr kernel module creates a pseudo file "/dev/cpu/x/msr" (with a unique x for each processor or processor core). A user with permissions to read and/or write to this file can use the file I/O API to access these registers. The msr-tools [6] package provides a reference implementation.