Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I believe you have some been misinformed about a few things. </p> <p>In modern terms clock speed is an <em>indication</em> of speed, not an actual measure of speed - so there is no reasonable way to estimate how long a single instruction may take. </p> <p>Your question is based on the assumption that all instructions are equal - they most certainly aren't, some CPU instructions get interpreted as sequences of micro-instructions on some architectures, and on others the timings may change. </p> <p>Additionally, you can't safely assume that on modern architectures that a repeated instruction will perform the same way, this depends on data and instruction caches, pipelines and branch prediction.</p> <p>The resolution of getTimeOfDay isn't anything like accurate enough to estimate the length of time required to measure single instructions, even CPU clock cycle counters (TSC on x86) are not sufficient. </p> <p>Furthermore, your operating system is a major source of error in estimation of such timings, context switches, power management, machine load and interrupts all have a huge impact. But even on a true hard real-time operating system (QNX or VxWorks), such measurements are still difficult, and require time and tools, as well as the expertise to interpret the results. On a General Purpose Operating System (windows or a basic Linux), you've got little to no hope of getting accurate measurements)</p> <p>The computational overhead and error of reading and storing the CPU cycle counts will also tend to dwarf the time required for one instruction. At minimum, I suggest you consider grouping several hundred or thousand instructions together.</p> <p>On deterministic architectures (1 cycle = 1 instruction) with no caches, like a PIC chip, you can do exactly what you suggest by using the clock multiplier, but even then to validate your measurements you would probably need a logic analyser (ie. you need to do this in hardware).</p> <p>In short, this is an extremely hard problem.</p>
    singulars
    1. This table or related slice is empty.
    1. POMeasuring time to perform simple instruction
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USAndrew Walker
    1. USAndrew Walker
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    1. This table or related slice is empty.
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload