Richard,
I did a few experiments using the example (jiq, I changed jiffies
to do_gettimeofday() ) from Linux Device
Driver, 2nd version (p196).
I have two machines m1 and m2. On m1, I run a timer queue (jiq)
module. Then I download a big file from m1 to m2. The timings are
different between before ftp and during ftp.
----------------------------------------
before ftp
----------------------------------------
time pid cpu command
420590 1 0 0 swapper
430580 1 0 0 swapper
440579 1 0 0 swapper
450579 1 0 0 swapper
460579 1 0 0 swapper
470579 1 0 0 swapper
480579 1 0 0 swapper
490579 1 0 0 swapper
500579 1 0 0 swapper
----------------------------------------
during ftp
----------------------------------------
time pid cpu command
370605 1524 0 in.ftpd
380645 0 0 swapper
390583 0 0 swapper
400667 0 0 swapper
410703 1524 0 in.ftpd
420679 0 0 swapper
430634 0 0 swapper
440624 0 0 swapper
450648 0 0 swapper
It shows that
timer queue is still not accurate. So
the conclusion of " you're guaranteed that the queue will run at the next
clock tick, thus eliminating latency caused by system load" is WRONG!!!
What is your opinion?
Xinwen Fu
On Wed, 3 Jul 2002, Richard B. Johnson wrote:
> On Wed, 3 Jul 2002, Xinwen - Fu wrote:
>
> > Hi, all,
> > I'm curious that if a network card interrupt happens at the same
> > time as the kernel timer expires, what will happen?
> >
> > It's said the kernel timer is guaranteed accurate. But if
> > interrupts are not masked off, the network interrupt also should get
> > response when a kernel timer expires. So I don't know who will preempt
> > who.
> >
> > Thanks for information!
> >
> > Xinwen Fu
>
> The highest priority interrupt will get serviced first. It's the timer.
> Interrupts are serviced in priority-order. Hardware "remembers" which
> ones are pending so none are lost if some driver doesn't do something
> stupid.
>
> Cheers,
> Dick Johnson
>
> Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
>
> Windows-2000/Professional isn't.
>
>
-
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