SCHED_4BSD bad interactivity on 7.0 vs 6.3

[Nate Eldredge]

On Sun, 13 Jul 2008, Nate Eldredge wrote:

> 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.

After trying this, I can't seem to reproduce the sound skipping behavior, 
unless I do something fairly extreme like "make -j 6".  But the mouse does 
seem to skip when a compile is running, so I do believe there is a 
regression.

-- 

Nate Eldredge
neldredge at math.ucsd.edu