Duration of Blocked Interrupts

[Alan Cox]

> interrupt lock sets I noticed a very definite correlation between reads
> from relatively slow devices (e.g. -- a SCSI CD-ROM) and a network
> deadlockup.  A lot of folks have reported and are still reporting
> bizarre problems on systems with AIC cards (although mine is now totally
> stable thanks to the network driver fix).

Any situation doing that and locking up is a Linux code bug simple and
plain. The constraint for IP service in the SMP kernel is 10mS - and you
get warnings and no fatal stop if its exceeded at.

> Even though my system is "stable", it could be taking quite a
> performance hit, and it would be very interesting to compare the
> coincidence of this sort of interrupt blocking and the "Too much work
> at..." messages in fast ethernet network drivers that occur when
> interrupts are stacked too deep when the driver is finally entered.

100Mbit cards have ring buffers often of about 20 frames - just servicing
a messier ISA interrupt will do as much delaying as the longer AIC handler
paths.

Alan


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