On 2012-05-09, Grant Edwards [off-list ref] wrote:

IOW: the real-time patch for 2.6.33.7 makes both the typical interrupt
latency and the CPU usage significantly worse.

Typical latency without the RT patch is 5-15us.

Typical latency with is 15-50us (I've never seen latency below 15us
with the RT patch).

Is this the expected behavior?

I've been loaned a clue by somebody on the OSADL mailing list: the RT
patches are for improving _user_space_ reponse, and may do so at the
expense of both CPU usage and interrupt latency.

As a result, I'm better off without the RT patch if what I care about
is interrupt latency.

Am right I correct in the following conclusions?

  * In 2.6.33.7, ISRs are really ISRs

  * In 2.6.33.7-rt30, ISRs are kernel threads.

  
-- 
Grant Edwards               grant.b.edwards        Yow! Don't hit me!!  I'm in
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