Re: em interrupt storm

From: Scott Long <scottl_at_samsco.org>
Date: Wed, 23 Nov 2005 01:50:09 -0700
Kris Kennaway wrote:
> On Wed, Nov 23, 2005 at 09:22:45AM +0100, Massimo Lusetti wrote:
> 
>>On Tue, 2005-11-22 at 22:03 -0500, Kris Kennaway wrote:
>>
>>>I am seeing the em driver undergoing an interrupt storm whenever the
>>>amr driver receives interrupts.  In this case I was running newfs on
>>>the amr array and em0 was not in use:
>>
>>[..]
>>
>>>This is on both 6.0-RELEASE and 6.0-STABLE.
>>
>>Wow, I've just ordered a machine with that same hardware to replace a
>>mailserver.
> 
> 
> Maybe it'll be OK if you disable the onboard NIC and use a different
> one.
> 
> Kris

This is apparently a side effect of how we process interupts, which is
different from Windows and Linux.  Since we mask the interrupt in the
APIC while the ithread runs, the Intel hardware tries to outsmart us and
continue delivering the interrupt via irq16.  There are been rumors
on ways to turn off this 'feature', but none of them seem to work. 
Since ithreads are integral to SMPng, and masking the APIC pins in
integral to making ithreads work, the solution will probably be to be
more aggressive in adopting MSI, and in doing filtered interrupt 
handlers that don't require the APIC to be masked.  Note that Solaris
and Darwin would likely exhibit the same problem since they handle
interrupts similar to us.

Scott
Received on Wed Nov 23 2005 - 07:50:53 UTC

This archive was generated by hypermail 2.4.0 : Wed May 19 2021 - 11:38:48 UTC