How fast does the kernel switches contexts, and does it dependent on type
and speed of cpu?
Where/how can I find current system tick rate for the Linux kernel context
switch?
Okay, vmstat show me the cs according to current load, what is the Maximum
tick rate?
A process requests a 1 microseconds sleep, or even 500 nanoseconds, how long
does it actually sleep, that is why I need to know max tick rate for context
switch for a given CPU.
-----Original Message-----
From: Mathieu Segaud [mailto:[email protected]]
Sent: Wednesday, June 02, 2004 3:52 PM
To: Garboua Nahil Y Contr WRALC/MASFE
Subject: Re: Context switch Tick
Garboua Nahil Y Contr WRALC/MASFE <[email protected]> writes:
> How fast does the kernel switches contexts, and does it dependent on type
> and speed of cpu?
> Where/how can I find current system tick rate for the Linux kernel
> context switch?
The context switch tick rate depends on many things:
- any time an interrupt is triggered, there is a ctx switch,
- schedule() performs a context switch if it finds a suitable process,
- schedule() is called on every blocking io that a process calls for,
so the rate is quite changing ;)
if you want to know the current ctx switch rate, use vmstat
vmstat 1 will gives a line per second on system info:
process statistics, io stats, memory stats, and cpu stats
the one you want is denoted "cs"
--
Mathieu Segaud
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On Wed, 2 Jun 2004, Garboua Nahil Y Contr WRALC/MASFE wrote:
> Okay, vmstat show me the cs according to current load, what is the Maximum
> tick rate?
> A process requests a 1 microseconds sleep, or even 500 nanoseconds, how long
> does it actually sleep, that is why I need to know max tick rate for context
> switch for a given CPU.
Can't you just measure it?
Script started on Wed Jun 2 16:48:51 2004
# ./tester
Testing CPU Speed (once at start of program)
CPU speed = 2803766848 Hz
Cycles to make the two function calls = 88
It took 55625156 cpu cycles or 19839.437091 microseconds.
# exit
Script done on Wed Jun 2 16:48:57 2004
That was for a usleep(1). Source attached.
Cheers,
Dick Johnson
Penguin : Linux version 2.4.26 on an i686 machine (5570.56 BogoMips).
Note 96.31% of all statistics are fiction.