SCHED_ULE with SMP broke libpthread/libthr on 5.4-RELEASE

Jonathan Noack noackjr at
Wed May 11 17:21:50 PDT 2005

On 05/11/05 18:28, Chris wrote:
> On 5/11/05, Marian Hettwer <MH at> wrote:
>>On Mi, 11.05.2005, 14:34, Steven Jurczyk sagte:
>>>**Using SCHED_ULE on SMP/HT machine broke applications which use
>>>libpthread/libthr, probably at context switching between threads... The
>>>applications simply hang and they aren't killable (kill -9 <pid> don't
>>>work).. Usually this also break kernel shutdown (can't flush some inodes
>>>or blocks)...
>>I have the same problem. My Kernel is basicly a GENERIC with SMP and ULE
>>added (4BSD removed).
>>([mhettwer at siteop-8] <~>)$ uname -a
>>FreeBSD 5.4-STABLE FreeBSD 5.4-STABLE #7: Wed May 11
>>12:03:35 CEST 2005
>>root at  i386
>>>This is very big problem for people who want use mysql_server on SMP
>>The MySQL server won't start and is not killable. I had to switch back to
>>SCHED_4BSD :-/
>>I would be available for testing packages, as this machine is not in
>>it's a dual xeon 2,8 ... you can find detailed information about it at:
> Seems the 4+ cpu crash fix might have broken it at a guess since RC4
> onwards it broke, I am interested in how this goes as I was planning
> on upgrading a SMP box to 5.4 and ULE this month.
> Have you guys tried this without SMP?

 From the sched_ule(4) man page:

As an experimental scheduler, sched_ule is not enabled by default due to 
a number of known issues, including weak performance with several known 
workloads, and reports of instability.  Deployment of sched_ule in 
production environments should be done cautiously."

The less well-known 5.4 Open Issues page 
( speaks to this as well:

"Many improvements have been made to the ULE scheduler in 6-CURRENT. 
These should be merged back to 5.4. The merging is done but ULE is still 
known to cause panics for some people, especially on SMP systems. Try it 
with extreme caution."

In other words, ULE is known to not be stable and will remain so until 
someone fixes it.

Jonathan Noack | noackjr at | OpenPGP: 0x991D8195
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