Experimental Physics and
Industrial Control System

"J. Lewis Muir" <[email protected]> · Sat, 30 Jan 2016 16:16:25 -0600

On 1/29/16 8:00 PM, Till Straumann wrote:
> On 01/29/2016 03:04 PM, J. Lewis Muir wrote:
>> On 1/29/16 3:54 PM, Till Straumann wrote:
>>> These would be my arguments:
>>>
>>> - it doesn't make much sense to use RT scheduling w/o memory locking
>>>   as this would hurt determinism. Thus, selectively disabling
>>>   mlockall() is a poor work-around.
>>
>> Hi, Till.
>>
>> True, but I think that just means the toggle is for the wrong thing.
>> It sounds like there should be a toggle for RT, not mlockall.  The RT
>> toggle would enable both the RT scheduling and the mlockall.
>
> That's what I suggested as an alternative - if you made it all
> the way to the bottom of my post ;-). I can see the value of a
> switch (or envvar) - but that should control the choice of scheduler
> together with mlock (and maybe even other features - such as priority
> inheritance - which could be desirable on certain platforms).
> The semantics should be "run as a RT app yes or no" with the default
> being "no"...

Hi, Till!

Sorry, I missed that!  Rereading your email, you start out by saying
that you think the current implementation is fine and no change
is required, and think that got me thinking that you were not for
any modification.  But I do see that at the end you said that if
anything you'd add a variable that is the runtime equivalent of
USE_POSIX_THREAD_PRIORITY_SCHEDULING.  I don't have experience with
POSIX threads, so that statement didn't immediately mean much to me, and
I think that's how I missed it.  Sorry about that.

I'd like to reiterate, though, that I think a toggle for "real-time" is
good, whereas a toggle that references thread priority scheduling is not
as good because it's too narrow.  The intent is to indicate whether or
not a real-time mode should be enabled, not how it's implemented.

Regards,

Lewis

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System