On 05/20/2013 12:27 PM, Ola Liljedahl wrote:
Predictable response times for specific threads. In the use cases I
am aware of, these threads would probably belong to the same process
and run core-affine on a specific core where as few as possible other
(kernel and user) threads and interrupts etc would also run. A number
of cores would follow this real-time model while other cores
preferably would keep the original Linux scheduling and
characteristics (to avoid introducing unexpected behaviour).
What benefits does SCHED_DEADLINE give in addition to stuff in
PREEMPT_RT?
Predictable response times are what SCHED_DEADLINE is about.
With SCHED_DEADLINE you can provide temporal guarantees up to 100% CPU
utilization that are not possibile with default real-time policies
(e.g. SCHED_FIFO/RR). This comes from the fact that SCHED_DEADLINE
achieves strong temporal isolation between tasks. You can reserve a
fraction of CPU time to your activities and be assured that no one else
can interfere with them. And this is critical also in a low loaded
system, if you want to be really safe against unexpected interferences.
Basically, with SCHED_DEADLINE you can make a feasibility study (no
deadline will be missed) of the system under development beforehand,
and be sure, at run-time, that the timing requirements will be met
under any circumstance. You can't do the same using only stuff already
in PREEMPT_RT.
Best,
- Juri
-- Ola
Ola Liljedahl, Networking System Architect, ARM Telephone: +46 706
866 373 Skype: ola.liljedahl
-----Original Message----- From: Amit Kucheria
[mailto:amit.kuche...@linaro.org] Sent: 20 May 2013 12:16 To: Ola
Liljedahl Cc: Mark Orvek; Patrick MacCartee; Mike Holmes;
linaro-networking; Lists linaro-dev; j.le...@sssup.it;
linaro-enterpr...@linaro.org; lng...@linaro.org Subject: Re: Deadline
scheduler inclusion in linux-linaro?
Ola,
Are you concerned with lower system-wide scheduling latency or with
predictable response times for a particular task?
I believe SCHED_DEADLINE with help with the later.
/Amit
On Mon, May 20, 2013 at 1:10 PM, Ola Liljedahl
<ola.liljed...@arm.com> wrote:
In my experience, networking is moving away from realtime
scheduling (and thus RTOS’es). There are some lingering
requirements for some of the processing in the wireless stack but
the main difficulty here is getting the scheduling latency down to
acceptable levels, e.g. five microseconds or so. Will
SCHED_DEADLINE help here?
-- Ola
Ola Liljedahl, Networking System Architect, ARM
Telephone: +46 706 866 373 Skype: ola.liljedahl
From: Amit Kucheria [mailto:amit.kuche...@linaro.org] Sent: 19 May
2013 11:51 To: Mark Orvek Cc: Patrick MacCartee; Mike Holmes;
linaro-networking; Lists linaro-dev; j.le...@sssup.it;
linaro-enterpr...@linaro.org; lng...@linaro.org Subject: Re:
Deadline scheduler inclusion in linux-linaro?
Similarly, the SCHED_DEADLINE patches shouldn't affect default
runtime scheduler behaviour unless a task uses the DEADLINE
policy.
However, I haven't studied the intersection of the Preempt RT and
SCHED_DEADLINE patches in source form yet. If they touch common
pieces of code, merging both in might be an ongoing effort. Juri,
do you know?
On Fri, May 17, 2013 at 8:11 PM, Mark Orvek <mark.or...@linaro.org>
wrote:
The PREEMPT_RT patchset is configurable. I believe the default is
PREEMPT_DESKTOP which is what most MV CGE customers use. Another
config options is PREEMPT_NONE but I believe its usage is rare.
Mark
On Fri, May 17, 2013 at 7:25 AM, Patrick MacCartee
<pmaccar...@mvista.com> wrote:
Will these be added in a way that makes them easy to remove? Many,
>95% don't use Preempt RT in Linux as it impacts network
performance and makes things very temperamental. You would think
people would just disable this RT, but when trying to isolate
issues it adds another variable to the mix. I believe Yocto has a
way of adding and removing RT patches that is some what straight
forward and preferable based on feedback from OEM's.
Just a thought,
Patrick
On Fri, May 17, 2013 at 6:34 AM, Mike Holmes
<mike.hol...@linaro.org> wrote:
In LNG you could end up with an interesting mix of preempt RT and
deadline patches making the analysis and benchmarking interesting
to interpret. In addition there are discussions about adding zero
overhead linux (ZOL) like features.
Mike
On Friday, May 17, 2013 6:08:20 AM UTC-4, David Rusling wrote:
Amit, an interesting proposal. I think that most of the LNG
steering committee is on this alias, but just in case, I'm adding
them to it... Dave
Amit Kucheria
17 May 2013 10:15
Hi all,
As part of our investigations into the Linux scheduler we've
interacted with Juri Lelli at the University of Pisa (cc'ed) who
is part of a group that is working on a DEADLINE scheduler[1] for
Linux[2].
While we're coming at this from a power managment angle[3], I
suspect that LEG and LNG already have real-world usecases that
would benefit from deadline scheduler found in other RTOSes.
So I think it makes sense to merge Juri's tree into linux-linaro
going forward to allow easier experimentation. Does LEG and LNG
have any interest in this at this point?
Juri has expressed an interest in maintaining a current branch of
the code that could be merged into our monthly release. In return,
real world usecases will improve his chances of getting the code
merged into mainline.
Regards, Amit
[1] http://retis.sssup.it/?q=node/35 [2]
https://lkml.org/lkml/2013/2/11/373 [3] Mostly involving
discussions at this point, no real engineering effort invested yet
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