Will RT patches be merged in main line?

[valdis.kletnieks at vt.edu]

On Mon, 28 May 2018 15:04:41 -0300, "Daniel." said:

> Does the RT patches have been merged in the main line? or, They will
> be merged at all?

Much of it has already been merged, the patchset used to be like 3-4 times the
size it is now.

> The main benefit of RT kernel is that decreases the latency right?

The point isn't to decrease the latency - realtime is about guaranteeing
a given process sufficient resources during each specified time interval.
Lowering the latency to open up more time is just one way to achieve that.

> I read that it make all parts of the kernel preemptive, is this right?

Well, that helps.  If the CPU is currently busy in a non-preemptive chunk
of code in a filesystem for the next 25ms, and an RT task needs at least
10ms of time during the next 20ms or a robot is going to crash into a wall
and halt an assembly line, you have a problem.

> Why aren't these parts preemptive in the main line?
> What is the impact of making these parts preemptive?
>
> My general concept is that RT kernel has decreased latency, but
> increased overhead, ... is this right?

And that's why most of the rest isn't merged.  It does add overhead and
decreases total system throughput.  And for 98% of the people who swear
up and down they need RT for their gaming/music/whatever, it turns out that
the current soft-RT code in the kernel is quite sufficient.

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