SCHED_4BSD bad interactivity on 7.0 vs 6.3

[Nate Eldredge]

On Sun, 13 Jul 2008, Kris Kennaway wrote:

> 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.

Okay.  I am in the process of recompiling all my ports, so after that is 
done I will boot with a GENERIC kernel and see what happens.

-- 

Nate Eldredge
neldredge at math.ucsd.edu