Richard Cochran wrote:
> On Sun, Apr 10, 2011 at 01:22:08PM +0200, Gilles Chanteperdrix wrote:
>> Also, about the performances, Xenomai 2.4 did not have the Xenomai
>> preemptible context switches. Maybe with FCSE, it results in reduced
>> latencies to disable this option in Xenomai 2.5.
> So, are you saying that XENO_HW_UNLOCKED_SWITCH=n might improve
> latency?
> The help for this option says...
>     This option reduces interrupt latency when costly cache and
>     TLB flushes are required to switch context, and may improve
>     concurrency on some SMP/multi-core systems as well.
>     You definitely want to enable that option on embedded ARM
>     platforms.
> so I am confused.

Is is a trade-off.

With this option enabled a context switch may be interrupted, this
improves interrupt latency, but at the expense of scheduling latency.

It makes a lot of sense without FCSE, when each context switch implies a
200us cache flush. A bit less with FCSE in guaranteed mode.


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