Interrupt statistics?

[Bernd Walter]

On Sun, Oct 12, 2003 at 09:55:03AM -0600, M. Warner Losh wrote:
> In message: <20031011234314.P23991 at root.org>
>             Nate Lawson <nate at root.org> writes:
> : Does anyone have recent statistics for interrupt latency and arrival
> : timings?
> 
> In -stable I know that we service fast interrupts in < 10us on a
> 666MHz machine 99.2% of the time.  I don't know about non-fast
> interrupts, but other results suggest that we'd do 99+% in less than
> 100us.  This is to the first instruction of the ISR.  The ISRs that
> I've been running typically run for 2us (since they do 30 instructions
> plus 2 ISA I/Os).

>From the serial application I did recently I know that writing 8 bytes
at 19200bps could pause the output for > 286us and < 429us after 5
bytes in about 50% tries with 16C552 ISA hardware.
Given the fact we get the interrupt before the last stop bit goes out
the real latency in handling is a multiple of this.
However - this was with an old current and I can retry with a recent
one once I get over the "no kernel output" problem.
If things should be acurate I can modify ISA hardware with a micro-
controller to do real measurements on a socket 7 HX board.

-- 
B.Walter                   BWCT                http://www.bwct.de
ticso at bwct.de                                  info at bwct.de