preemption stable under 5.3?

Julian Elischer julian at elischer.org
Mon Nov 8 13:11:06 PST 2004



Robert Watson wrote:

>On Mon, 8 Nov 2004, Mipam wrote:
>
>  
>
>>Thanks for your reply, okay, then i'd like to enable preemption.  I
>>noticed it's not in the GENERIC kernel config file.  So: options
>>PREEMPTION would suffice to enable it i guess?  Any experience with
>>preemption. noticable changes?  So the problem: "PREEMPTION triggers
>>frequent hangs" is resolved?  Btw, is RELENG_5 also stable or only for
>>early adopters?  I really would like to see ule working stable in
>>combination with preemption, but in 5.3 it won't happen. Maybe ule will
>>be enabled later in the 5 series? 
>>    
>>
>
>There was a series of bugs in the scheduler which got tickled by
>preemption; I'm unclear as to whether they were all resolved before 5.3 or
>whether they require fixes in HEAD that haven't yet been merged.  It may
>well be safe, but I make no promises.  Hopefully we can trick Julian or
>John into responding to this thread. :-)  Having it off by default on 5.3
>is certainly the more conservative (and reasonable) position, but if it
>helps your environment and appears stable, there should be no reason not
>to turn it on.  It should substantially improve latency in interrupt
>processing as well as packet processing.
>

I think that PREEMPTION with SCHED_4BSD might be ok..
It's hard to say because it's always harder to prove something correct 
than to prove it broken :-)

Hopefully with the rush off, we can sit down and try "prove it ok" and 
take some cleanup passes over it.
I still owe my wife a significant "chunk-o-time" (TM) however so count 
me out for a while .
Hopefully however ups@ is coming online again this week.






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