SCHED_4BSD bad interactivity on 7.0 vs 6.3

[Nate Eldredge]

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.

-- 

Nate Eldredge
neldredge at math.ucsd.edu