SCHED_4BSD bad interactivity on 7.0 vs 6.3
Kris Kennaway
kris at FreeBSD.org
Sun Jul 13 01:11:23 UTC 2008
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.
Kris
> 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.
>
> SCHED_ULE is much better, so I've switched over. But it's not the
> default yet, and most people are still going to be using SCHED_4BSD. It
> used to be acceptable but now it isn't. Does anyone know why it's
> regressed so badly?
>
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