* duration of udelay differs with activated realtime-preempt patch?
@ 2005-11-25 10:26 Schultheiss, Christoph
2005-11-25 13:28 ` Steven Rostedt
0 siblings, 1 reply; 3+ messages in thread
From: Schultheiss, Christoph @ 2005-11-25 10:26 UTC (permalink / raw)
To: linux-kernel
kernel: 2.6.14 with and without the realtime-preempt patch
hi list,
after measuring the duration of the function udelay (with oscilloscope
at parallel port), I figured out that udelay (5usec) with activated
realtime- preempt patch lasts a little bit longer. Without the patch the
time is exact.
All kernel debug switches are turned off at compile time.
Can anyone suggest why this happens?
christoph
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: duration of udelay differs with activated realtime-preempt patch?
2005-11-25 10:26 duration of udelay differs with activated realtime-preempt patch? Schultheiss, Christoph
@ 2005-11-25 13:28 ` Steven Rostedt
2005-11-25 13:55 ` Ingo Molnar
0 siblings, 1 reply; 3+ messages in thread
From: Steven Rostedt @ 2005-11-25 13:28 UTC (permalink / raw)
To: Schultheiss, Christoph; +Cc: john stultz, Ingo Molnar, linux-kernel
On Fri, 2005-11-25 at 11:26 +0100, Schultheiss, Christoph wrote:
> kernel: 2.6.14 with and without the realtime-preempt patch
>
> hi list,
>
> after measuring the duration of the function udelay (with oscilloscope
> at parallel port), I figured out that udelay (5usec) with activated
> realtime- preempt patch lasts a little bit longer. Without the patch the
> time is exact.
> All kernel debug switches are turned off at compile time.
> Can anyone suggest why this happens?
Well, the -rt patch, has changed the udelay function. BTW, you are
using the constant udelay, right? Maybe an example of the code you used
to test might be useful.
Ingo or John?
-- Steve
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: duration of udelay differs with activated realtime-preempt patch?
2005-11-25 13:28 ` Steven Rostedt
@ 2005-11-25 13:55 ` Ingo Molnar
0 siblings, 0 replies; 3+ messages in thread
From: Ingo Molnar @ 2005-11-25 13:55 UTC (permalink / raw)
To: Steven Rostedt; +Cc: Schultheiss, Christoph, john stultz, linux-kernel
* Steven Rostedt <rostedt@goodmis.org> wrote:
> > after measuring the duration of the function udelay (with oscilloscope
> > at parallel port), I figured out that udelay (5usec) with activated
> > realtime- preempt patch lasts a little bit longer. Without the patch the
> > time is exact.
> > All kernel debug switches are turned off at compile time.
> > Can anyone suggest why this happens?
>
> Well, the -rt patch, has changed the udelay function. BTW, you are
> using the constant udelay, right? Maybe an example of the code you
> used to test might be useful.
>
> Ingo or John?
yes, i found this problem too, a week ago or so. It's due to the GTOD
changes to i386's __delay() function. Does it still occur with -rt15
[which has the -B11 GTOD patchset] ?
Ingo
^ permalink raw reply [flat|nested] 3+ messages in thread
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2005-11-25 10:26 duration of udelay differs with activated realtime-preempt patch? Schultheiss, Christoph
2005-11-25 13:28 ` Steven Rostedt
2005-11-25 13:55 ` Ingo Molnar
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