Big problems with 7.1 locking up :-(

[Robert Watson]

On Fri, 9 Jan 2009, Garance A Drosihn wrote:

> At 2:39 PM -0500 1/9/09, Robert Blayzor wrote:
>> On Jan 8, 2009, at 8:58 PM, Pete French wrote:
>>> I have a number of HP 1U servers, all of which were running 7.0 perfectly 
>>> happily. I have been testing 7.1 in it's various incarnations for the last 
>>> couple of months on our test server and it has performed perfectly.
>> 
>> I noticed a problem with 7.0 on a couple of Dell servers.  [...] We've 
>> since then compiled the kernel under the BSD scheduler to rule that out, 
>> and so far so good.
>> 
>> Since ULE is now default in 7.1 and not in 7.0, perhaps you can try that?
>
> FWIW, the other guy I know who is having this problem had already switched 
> to using ULE under 7.0-release, and did not have any problems with it.  So 
> *his* problem was probably not related to SCHED_ULE, unless something has 
> recently changed there.
>
> Turns out he hasn't reverted back to 7.0-release just yet, so he's going to 
> try SCHED_4BSD and see if that helps his situation.

Scheduler changes always come with some risk of exposing bugs that have 
existed in the code for a long time but never really manifested themselves. 
ULE is well shaken-out, having been under development for at least five years, 
but it is possible that some problems will become visible as a result of the 
switch.  I would encourage people to stick with ULE, but if you're having a 
stability problem then experimenting with scheduler as a variable that could 
be triggering the problem may well be useful to help track down the bug.  Most 
of the time the bugs will not be in ULE itself, rather, triggered because ULE 
will change the ordering or balancing of work in the system, so we should try 
to avoid situations where people switch to 4BSD from ULE and stick with it 
rather than getting the underlying problem fixed!

Robert N M Watson
Computer Laboratory
University of Cambridge