Guest Lecture TDDD07 Real-Time Systems Real world Real ...simna73/teaching/REAP/HT14/Ericsson.pdf · ›Main business at Ericsson in Linköping is related to 2G (GSM) and 4G (LTE)

Slide title

70 pt

CAPITALS

Slide subtitle

minimum 30 pt

Guest Lecture TDDD07 Real-Time Systems

Real world Real-Time Beautiful Real-Time

Patrik Sandahl, Ericsson

Slide title

44 pt

Text and bullet level 1

minimum 24 pt

Bullets level 2-5

minimum 20 pt

Characters for Embedded font: !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~¡¢£¤¥¦§¨©ª«¬®¯°±²³´¶·¸¹º»¼½ÀÁÂÃÄÅÆÇÈËÌÍÎÏÐÑÒÓÔÕÖ×ØÙÚÛÜÝÞßàáâãäåæçèéêëìíîïðñòóôõö÷øùúûüýþÿĀāĂăąĆćĊċČĎďĐđĒĖėĘęĚěĞğĠġĢģĪīĮįİıĶķĹĺĻļĽľŁłŃńŅņŇňŌŐőŒœŔŕŖŗŘřŚśŞşŠšŢţŤťŪūŮůŰűŲųŴŵŶŷŸŹźŻżŽžƒȘșˆˇ˘˙˚˛˜˝ẀẁẃẄẅỲỳ–—‘’‚“”„†‡•…‰‹›⁄€™ĀĀĂĂĄĄĆĆĊĊČČĎĎĐĐĒĒĖĖĘĘĚĚĞĞĠĠĢĢĪĪĮĮİĶĶĹĹĻĻĽĽŃŃŅŅŇŇŌŌŐŐŔŔŖŖŘŘŚŚŞŞŢŢŤŤŪŪŮŮŰŰŲŲŴŴŶŶŹŹŻŻȘș−≤≥fifl

ΆΈΉΊΌΎΏΐΑΒΓΕΖΗΘΙΚΛΜΝΞΟΠΡΣΤΥΦΧΨΪΫΆΈΉΊΰαβγδεζηθικλνξορςΣΤΥΦΧΨΩΪΫΌΎΏ

ЁЂЃЄЅІЇЈЉЊЋЌЎЏАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯАБВГДЕЖЗИЙКЛМНОПРСТУФХЦЧШЩЪЫЬЭЮЯЁЂЃЄЅІЇЈЉЊЋЌЎЏѢѢѲѲѴѴҐҐәǽẀẁẂẃẄẅỲỳ№

Do not add objects or

text in the footer area Ericsson Real-Time | Public | © Ericsson AB 2014 | 2014-12-08 | Page 2

› Ericsson

› Real World Real-Time

– Separate real-time and throughput oriented workloads

› Beautiful Real-Time

› Lessons learned

Outline

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Not making phones anymore, but everything else in mobile

networks

› Main business at Ericsson in Linköping is related to 2G

(GSM) and 4G (LTE).

› Most Ericsson equipment contain a fair amount of real-

time.

Ericsson

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Real-time workloads often react on events.

– E.g. timers, internal messages or network traffic.

› Real-time workloads often show concurrency.

– E.g. a mobile radio network serving several users at the same time.

Real-Time Workloads

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Throughput workloads often react on events.

– E.g. timers, internal messages or network traffic.

› Throughput workloads often show concurrency.

– E.g. a mobile radio network serving several users at the same time.

Throughput Workloads

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Real-time applications must produce its result within time.

– The right answer given at the wrong time is a wrong answer.

› Throughput oriented applications often care about time too.

But much more relaxed, e.g.:

– 97.5 percent of the requests should be handled in less than 100 ms.

– A late answer is just a late answer, not a wrong answer.

So, what’s the difference?

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› In the real world, a system often is built up of both real-time

and throughput oriented workloads.

› One particular challenge is to correctly identify different

types of workloads and make sure that they can’t interfere

in bad ways.

Real World Real-Time

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Throughput oriented workloads prefer a lot of dynamic

rubber bands in order to fully utilize work units.

– Buffers.

– Caches.

– Laziness.

– Reordering.

– Speculation.

› Real-time oriented workloads really hate all the above as it

gives unpredictability.

Different Preferences

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






› Massive simulation of LTE UEs (think: 4G smartphones).

– The purpose is testing of LTE base stations.

› The simulator is implementing the LTE network stack from

(almost) antenna interface up to TCP/IP.

› The parts of the LTE network stack close to the antenna

must be tightly synchronized with the timings for the

antennas.

– The antennas work with timeslots called “subframes”. Each

subframe is 1 ms.

› Other parts of the LTE network stack are more throughput

oriented.

Case study

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






LTE Ue – subframe synchronization

DL-data or UL-grant received at time ‘t’ DL-ACK or UL-data “on air” at time ‘t+4’

Period for matching UL (from UE to base station) and DL (from base station to UE)

1 ms 1 ms Must match the millisecond subframe

exactly at both “read” and “write”

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






LTE Ue stack

MAC

PHY

RLC

PDCP

IP

Synchronized with subframes

at downlink

Synchronized with subframes on uplink

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Legend – UE DL

RLC: Throughput workload, less time-critical

MAC: Highly time-critical

PHY: Highly time-critical

Completely failed subframe

Processing started late. Time constraints met

Completely successful subframe

Time trigger for subframe – should be close to start

Control returned to the timer event handler

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Tight coupling Real-Time <=> Throughput

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Loose Coupling Real-Time <=> Throughput

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Lessons Learned

› Identify what parts of your system that are real-time, and

what parts that are throughput oriented.

› Make sure that those parts are loosely coupled, otherwise

the throughput oriented stuff will destroy your real-time.

– Message passing is a nice tool for loose coupling.

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Beautiful Real-Time

› Does it matter if a program is “beautiful” or not?

› What do YOU think?

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Accidental Complexity

› Accidental (or incidental) complexity is complexity that arises in

computer programs or their development process which is non-

essential to the problem to be solved. While essential complexity is

inherent and unavoidable, accidental complexity is caused by the

approach chosen to solve the problem.

Accidental complexity is to be minimized in any good architecture,

design, and implementation; excessive accidental complexity is an

example of an anti-pattern.

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Accidental Complexity

› Many real-time programs – as well as throughput oriented

programs – often are concurrent, asynchronous and event

driven.

› But the most of the tools and languages used for software

development is best suited for sequential, synchronous and

batch oriented tasks.

› This is a major source of accidental complexity.

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






fs.readdir(source,function(err, files) {

if (err) {

console.log('Error finding files: ' + err)

} else {

files.forEach(function(filename, fileIndex) {

console.log(filename)

gm(source + filename).size(function(err, values) {

if (err) {

console.log('Error identifying file size: ' + err)

} else {

console.log(filename + ' : ' + values)

aspect = (values.width / values.height)

widths.forEach(function(width, widthIndex) {

height = Math.round(width / aspect)

console.log('resizing ' + filename +

'to ' + height + 'x' + height)

this.resize(width, height).write(destination +

'w' + width + '_' + filename,function(err) {

if (err)

console.log(“Error writing file:” + err)})}.bind(this))

}

})

})

}

}

Slide title

44 pt


minimum 24 pt

Bullets level 2-5

minimum 20 pt






Ways towards Beautiful Real-Time

› Learn and embrace the actor programming model. Actors

are very light weight processes, handled outside the

operating system.

› The main benefit is that each actor handle one single

interaction, and can thus be programmed in a simple

synchronous and sequential style.

› Excellent implementations in many functional programming

languages. E.g.:

– Erlang

– Scala

– Haskell

› Not really actors, but ENEA/OSE (in C) is very nice for

“bare bones” environments.

Documents

Guest Lecture TDDD07 Real-Time Systems Real world Real ...simna73/teaching/REAP/HT14/Ericsson.pdf · ›Main business at Ericsson in Linköping is related to 2G (GSM) and 4G (LTE)