RE: [Patch] speed up interrupt handling

From: Peter Chubb <peter_at_chubb.wattle.id.au>
Date: 2004-02-28 08:27:40
>>>>> "David" == David Mosberger <davidm@napali.hpl.hp.com> writes:

>>>>> On Fri, 27 Feb 2004 18:44:38 +1100, Peter Chubb <peter@chubb.wattle.id.au> said:
>>>>> "Scott" == Scott Feldman <Feldman> writes:

>>>> Is this related to NAPI?

>>>> I'll assume "the gigabit" card is e1000:

Peter> Nope, DP83820.  I'm benchmarking a driver that runs in
Peter> userspace against the in-kernel driver; both benefit from the
Peter> interrupt speedup.

David> So why is irq enabling/disabling on the critical path for this
David> driver?

Because IRQs are disabled for every hardware interrupt, and enabled after each
interrupt returns.  So the latency between hardware interrupt and the
driver seeing the interrupt *was* (prepatch) around 5 microseconds;
minimum latency between interrupts was around 10 microseconds.
This is time on a busy system to run out of receive buffers (you can
get a new packet every 640ns with minimum-sized packets, and it takes
time to process each packet)

With the patch minimum time between interrupts should drop to around 2us,
but I need to measure it again.

--
Dr Peter Chubb  http://www.gelato.unsw.edu.au  peterc AT gelato.unsw.edu.au
The technical we do immediately,  the political takes *forever*
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Received on Fri Feb 27 16:42:29 2004

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