Context switch in CPU

Question

suppose the time it takes to switch between user and kernel modes is t1 and to switch between two processes is t2.Which is greater t1 or t2?

Homework? If it is, please be up front about that.

Adam Robinson
– Adam Robinson

2011-02-13 18:31:34 +00:00
Commented Feb 13, 2011 at 18:31 — Adam Robinson
– Adam Robinson, Commented Feb 13, 2011 at 18:31

Andrey · Accepted Answer · 2011-02-13 18:29:22Z

4

I think t2 is always larger, because process switch happens via kernel mode.

answered Feb 13, 2011 at 18:29

Andrey

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Jerry Coffin · Accepted Answer · 2011-02-13 18:29:24Z

3

Theoretically it depends on the platform. In practice, a switch from one process to another typically goes from the original process to kernel mode, then the kernel decides which process to schedule next, then there's a switch from kernel mode to user mode running the second process.

As such, switching from one process to another includes a switch from user- to kernel-mode, plus more, so it'll be slower.

answered Feb 13, 2011 at 18:29

Jerry Coffin

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John Zwinck · Accepted Answer · 2011-02-13 18:24:55Z

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It depends on the platform. You should profile yours.

answered Feb 13, 2011 at 18:24

John Zwinck

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1 Comment

John Zwinck Over a year ago

You might try making a simple system call in a loop and seeing how fast that is. Then run a program which calls sched_yield() a lot and see how that goes (how much time until it gets control back). I think you could learn something this way, with some refinements. That said, your answer about t2 being longer in general seems intuitively sensible.

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