Re: Linux 2.4.17 vs 2.2.19 vs rml new VM

From: Dieter Nützel (
Date: Wed Jan 02 2002 - 18:14:24 EST

On Tuesday, 2. January 2002 20:50, Alan cox wrote:
> > I find the low latency patch makes a noticeable
> > difference in e.g. q3a and rtcw - OTOH I have
> > not been able to discern any tangible difference
> > from the stock kernel when using -preempt.
> The measurements I've seen put lowlatency ahead of pre-empt in quality
> of results. Since low latency fixes some of the locked latencies it might
> be interesting for someone with time to benchmark
> vanilla
> low latency
> pre-empt
> both together

Don't forget that you have to use preempt-kernel-rml + lock-break-rml to
achieve the same (more) than the latency patch.

Taken from Robert's page and running it for some weeks, now.

Lock breaking for the Preemptible Kernel
With the preemptible kernel, the need for explicit scheduling points, like in
the low-latency patches, are no more. However, since we can not preempt while
locks are held, we can take a similar model as low-latency and "break" (drop
and immediately reacquire) locks to improve system response. The trick is
finding when and where we can safely break the locks (periods of quiescence)
and how to safely recover. The majority of the lock breaking is in the VM and
VFS code. This patch is for users with strong system response requirements
affected by the worst-case latencies caused by long-held locks.


Dieter Nützel
Graduate Student, Computer Science

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