Re: interrupt latency/700microsecs

[William Lee Irwin III <wli@holomorphy.com>]

On Mon, May 27, 2002 at 08:30:06PM +0400, Muthal Sangam wrote:
> On kernel 2.4.7, AMDK6 @ 450MHz processor, is it possible to get latency
> fluctuations of upto 700microsecs for running the timer interrupt, due to
> interrupts being disabled ?
> I am using the time stamp counter and reading it at the start of the timer
> interrupt and measuring the cycles elapsed between two inovocations of it.
> The number of cycles elapsed is ~4500225, but sometimes it increases to as
> high as 4848032. Can i conclude that this difference is due to interrupts
> being disabled in critical sections ? ( I think i am making some mistake :-)

IIRC there have been prior reports of excessive interrupt disablement
in 2.4.x, and also IIRC it was reported against a more recent kernel.
I think it was suspected there are bug(s) where some code is leaving
interrupts off and someone later unconditionally turns them back on.

Any chance you could upgrade to a more recent kernel and try to
reproduce there? There have been a number of critical bugfixes since 2.4.7
(and although none are particularly pertinent to this issue, people would
probably rather field bug reports for 2.4.19-pre* than 2.4.7).


Cheers,
Bill