SCHED_DEADLINE (what it does and doesn't do, yet).

Transcription

1 SCHED_DEADLINE (wha i does and doesn' do, ye). Juri Lelli Deparmen of Auomaic Conrol Lund Universiy (Sweden), May 5h 2014 TeCIP Insiue, Scuola Superiore San'Anna Area della Ricerca CNR, Via G. Moruzzi Pisa, Ialy

2 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 2/39

3 Talk Maerials available for download from my sie: hp://reis.sssup.i/~jlelli/alks/lund050514/ 3/39

4 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 4/39

5 OS kernels and schedulers Linux is an OS kernel (no a full OS as i doesn' include FS uiliies, WM, GUIs, compilers, ec.) Composed by several sub-sysems One of which is he Scheduler Decides which process o run where and when, achieving an apparen simulaneous execuion of muliple processes on he same shared HW Tradiionally General Purpose: didn' include proper Real-Time scheduling feaures 5/39

6 A new scheduling policy/class SCHED_DEADLINE SCHED_DEADLINE SCHED_FIFO SCHED_FIFO SCHED_RR SCHED_RR SCHED_BATCH SCHED_BATCH SCHED_NORMAL SCHED_NORMAL SCHED_IDLE SCHED_IDLE deadline.c r.c fair.c Linux scheduler 6/39

7 An hisory of LKML poss sared wihin he ACTORS EU projec (2008) originally developed and mainained by Dario Faggioli e al. hen I swiched in (v4 April 6h, 2012) 9 versions posed Merged by Linus on Sun, 2 Feb :12:22 WE ARE IN MAINLINE!!! YAY!!! Curren sable is Linux /39

8 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 8/39

9 Predicabiliy and Isolaion 4 CPU-hog processes (i.e. while(1)) on 4 CPUs SCHED_NORMAL (defaul Linux scheduling policy) SCHED_DEADLINE finer-grained conrol over asks scheduling asks don' inerfere wih each oher 9/39

10 Sporadic ask model acivaion/wakeup absolue deadline sar ime compuaion ime relaive deadline period 10/39

11 Real-ime scheduling algorihms asks are execued in prioriy order Rae Monoonic (RM) asks wih shorer periods have higher prioriies Earlies Deadline Firs (EDF) asks wih earlier deadlines have higher prioriies 11/39

12 Saic vs. Dynamic (UP) τ1 2 every τ2 4 every 7 97% overall load τ τ2 RM no more han 69% overall load (when n is big) τ1 EDF can achieve 100% τ2 12/39

13 Deadline scheduling (EDF) τ1 5 every 9 τ2 2 every 6 ~88.9% overall load τ1 τ2 13/39

14 Deadline scheduling (EDF) τ1 blocks jus afer he second acivaion τ1 resumes wih he hird insance of τ2 τ1 τ2 14/39

15 Deadline scheduling (EDF) τ1 second job behaves bad τ1 τ2 15/39

16 Reservaion Based scheduling Concurren real-ime asks compee for resources (CPU ime) Resource Reservaion mechanism A ask is allowed o execue for: Q ime unis (runime) in every inerval of lengh P (period) Task uilizaion is U=Q/P 16/39

17 Reservaion Based scheduling Each reservaion has is own dynamic deadline (Consan Bandwidh Server) Reservaions are scheduled by EDF EDF gives higher prioriy o more urgen asks CBS slows down (or hroles) misbehaving asks EDF + CBS ensures emporal isolaion 17/39

18 EDF + CBS plain EDF (block/unblock) τ1 τ2 τ1 blocks jus afer he second acivaion τ1 resumes wih he hird insance of τ2 (CBS unblock rule applied) τ1 τ2 18/39

19 EDF + CBS plain EDF (bad ask) τ1 τ2 τ1 second job behaves bad once budge exaused, delay unil nex acivaion period τ1 τ2 19/39

20 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 20/39

21 Adds new syscalls: sched_sear(), sched_gear() sysem wide deadline bandwidh managemen coupled wih RT /proc/sys/kernel/sched_r_runime_us /proc/sys/kernel/sched_r_period_us r_bw is enforced a runime (r hroling) dl_bw is reserved wih AC, and enforced a runime 21/39

22 Symmeric Muli-Processors DL asks are kep ino CPU-specific runqueues implemens Global EDF (DL asks are migraed among runqueues o achieve): on an M-CPU sysem he M earlies DL ready asks are always running; affiniy/cpuses seings of all he DL asks is always respeced 22/39

23 SMP ready! 4 CPU-hog processes (i.e. while(1)) on 4 CPUs + 1 more afer a while... new cpuhog5 arrival causes a migraion for cpuhog2 sysem sabilizes ino a new condiion, similar o pariioned scheduling 23/39

24 Inerface sruc sched_ar { u32 size; u32 sched_policy; u64 sched_flags; /* SCHED_NORMAL, SCHED_BATCH */ s32 sched_nice; /* SCHED_FIFO, SCHED_RR */ u32 sched_prioriy; /* SCHED_DEADLINE */ u64 sched_runime; u64 sched_deadline; u64 sched_period; }; in sched_sear(pid_ pid, cons sruc sched_ar *ar, unsigned in flags); in sched_gear(pid_ pid, cons sruc sched_ar *ar, unsigned in size, unsigned in flags); 24/39

25 Example #include <sched.h>... sruc sched_ar ar; ar.size = sizeof(sruc ar); ar.sched_policy = SCHED_DEADLINE; ar.sched_runime = ; ar.sched_period = ; ar.sched_deadline = ar.sched_period;... if (sched_sear(geid(), &ar, 0)) perror("sched_sear()");... 25/39

26 RR over sporadic ask model simple rule of humb, see lieraure for opimal seings... average runime [ns] deadline [ns] period [ns] 26/39

27 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 27/39

28 Clone and Compile Clone Linus' repo gi clone gi://gi.kernel.org/pub/scm/linux/kernel/gi/orvalds/linux.gi Configure, compile and insall cp /boo/config `uname r`.config yes "" make oldconfig make j `ca /proc/cpuinfo grep processor wc l awk '{prin $1 + 1}'` sudo make modules_insall insall updae iniramfs c k VERSION && updae grub or wai for nex Ubunu, Fedora, ec. release... 28/39

29 Tes r-app gi clone app.gi cd r app./auogen.sh (requires auoools)./configure wih deadline wih json make && make insall r app :10000:d D10 or r app askse.json schedool gi clone gi@gihub.com:jlelli/schedool dl.gi cd schedool dl make && make insall schedool E : e yes 29/39

30 encapsulae a yes process inside a 10 ms, 100ms reservaion schedool E : e yes see execuion race wih kernelshark 30/39

31 encapsulae a yes process inside a 10 ms, 100ms reservaion schedool E : e yes 10 ms 100 ms 31/39

32 Saic vs. Dynamic (UP) τ1 2 every τ2 4 every 7 97% overall load τ τ RM no more han 69% overall load (when n is big) WITH r-app! τ1 EDF can achieve 100% τ2 32/39

33 Provide QoS o VMs KVM creaes one hread per VPCU and one hread per VM doing I/O encapsulae VPCU hreads inside reservaions o provide QoS guaranees 33/39

34 Provide QoS o VMs a single-core VM runs a CPU-bound aciviy: sysbench, calculaion of prime numbers up o a cerain value we vary he reservaion budge of is VCPU 34/39

35 Provide QoS o VMs a single-core VM runs a nework aciviy: iperf server wih exernal requess from a clien running on differen HW we vary he reservaion budge of is VCPU 35/39

36 Provide QoS o VMs vm1 (visualized) runs iperf server, vm2 sysbench load of vm2 doesn' affec vm1 performance vm2 reservaion vm1 reservaion 36/39

37 Provide QoS o VMs boh vm1 (visualized) and vm2 run iperf servers we sill have a cerain degree of isolaion (probably beer wih dedicaed HW or differen configuraions) vm2 reservaion vm1 reservaion 37/39

38 Ouline Basics and saus Wha SCHED_DEADLINE is implemening API and usage Demos 38/39

39 Thanks! Quesions? 39/39