SCHED_4BSD bad interactivity on 7.0 vs 6.3

[Kris Kennaway]

Nate Eldredge wrote:
> On Sun, 13 Jul 2008, Kris Kennaway wrote:
> 
>> Nate Eldredge wrote:
>>> Hi folks,
>>>
>>> Hopefully this is a good list for this topic.
>>>
>>> It seems like there has been a regression in interactivity from 
>>> 6.3-RELEASE to 7.0-RELEASE when using the SCHED_4BSD scheduler.  
>>> After upgrading my single-cpu amd64 box, 7.0 has much worse latency.  
>>> When running a kernel compile, there is a noticeable lag to echo my 
>>> typing or scroll my browser windows, and playing an mp3 frequently 
>>> cuts out for a second or two.  This did not happen on 6.3-RELEASE.
>>
>> Are you sure it's not the x.org server bug that was present in the 
>> version shipped with 7.0?  Update to the latest version and see if 
>> your X interactivity improves.
> 
> Yes, I had not yet upgraded my x.org port when testing this, so it was 
> the same x.org that was fine under 6.3.  Also:
> 
>>> I wrote a small program which forks two processes that run 
>>> gettimeofday() in a tight loop to see how long they get scheduled 
>>> out.  On 6.3 the maximum latency is usually under 100 ms.  On 7.0 it 
>>> is 500 ms or more even when nothing else is running on the system.  
>>> When a compile is also running it is sometimes 1400 ms or more.
> 
> This test shows a difference even in single user mode, when X is not 
> running at all.
> 

It shows *a* difference, but perhaps not the *same* difference.  Please 
humour me and rule it out.

Kris