kern/119487: page fault in em taskq with polling enabled

[Remko Lodder]

The following reply was made to PR kern/119487; it has been noted by GNATS.

From: "Remko Lodder" <remko at elvandar.org>
To: =?iso-8859-1?Q?=C5ke_Wallebom?= <ake at ake.nu>
Cc: freebsd-gnats-submit at freebsd.org
Subject: Re: kern/119487: page fault in em taskq with polling enabled
Date: Wed, 9 Jan 2008 17:29:30 +0100 (CET)

 > FreeBSD dunder 7.0-RC1 FreeBSD 7.0-RC1 #2: Tue Jan  8 22:29:24 CET 2008
 >  removed at dunder:/usr/obj/usr/src/sys/CUSTOM  amd64
 >
 >>Description:
 > I got a page fault with 'current process' being 'em0 taskq' while
 > transferring about 200 GB of data from an ftp server to my FreeBSD box via
 > Gigabit LAN.
 >
 > I had compiled my kernel with DEVICE_POLLING and HZ=2000, and
 > kern.polling.enable was set to 1 (I noticed later that this was
 > deprecated).
 >
 > The files were transfered onto a ZFS pool on a GELI-device (1TB
 > SATA2-drive).
 >
 > After transferring 150 GB i got the above error and the kernel panic'ed.
 >
 > Sadly, I can't remember the whole error message.
 >
 > More about the machine:
 >
 > Core 2 Duo E6750
 > 4 GB RAM
 > Three Intel PRO/1000 GT Desktop NICs (Single port cards)
 >>How-To-Repeat:
 > I really don't know...
 >
 > Hasn't happened again - but I have now recompiled the kernel with just
 > 'POLLING' set, using default HZ now. And now i don't enable polling via
 > sysctl but via ifconfig xxx polling.
 >
 > Transfered 180 GB and did not crash. So I guess I'm just reporting this as
 > a curiosity for the em driver developer(s).
 >>Fix:
 > Decrease the HZ value?
 > Set polling via ifconfig instead of kern.polling.enable?
 >
 
 One of the things: dont use polling with em cards, it's not needed and
 could have negative impact on your machine. Also, if you get a crash,
 please try to obtain a kernel crashdump so that we can see what is going
 on and understand it and fix it ;-)
 
 You can see more details about that on
 http://www.freebsd.org/doc/en/books/developers-handbook/kerneldebug.html
 
 Without it, it's just looking in the blind.
 
 In addition; can you test this without polling enabled at all?
 
 Cheers,
 Remko
 
 -- 
 /"\   Best regards,                      | remko at FreeBSD.org
 \ /   Remko Lodder                       | remko at EFnet
  X    http://www.evilcoder.org/          |
 / \   ASCII Ribbon Campaign              | Against HTML Mail and News