UK Condor Week NeSC – Scotland – Oct 2004 Condor Team Computer Sciences Department University of Wisconsin-Madison The Bologna Batch System: Flexible Policy with Condor

2 The Bologna Batch System Custom batch scheduling system for local users at INFN in Bologna, Italy. Istituto Nazionale di Fisica Nucleare Dr. Paolo Mazzanti initiated the idea. Implement on a small subset of machines within the larger nationwide INFN Condor pool: INFN Condor Pool: ~300 CPUs INFN-Bologna Condor: ~100 CPUs Bologna Batch System: ~50 CPUs

3 Where We Started Basic Condor Policy Opportunistic resources Jobs only run when machines are otherwise idle Jobs can be preempted for machine owners or higher- priority users Fair-share across INFN pool Highest priority user in the pool gets first crack at a given resource The more you use, the worse your priority becomes Some problems: Long-running vanilla jobs (with no checkpointing) were frequently preempted before running to completion Users dislike waiting for a resource if they only want to run a short job High-priority users from other INFN sites running on local resources while lower-priority local users wait.

4 BBS Policy Requirements Prioritize local work Share resources, but run outside jobs as backfill Treat local servers as dedicated resources for local jobs, but opportunistic resources for other jobs. Run outside Condor jobs only if the server is idle. Run local batch jobs regardless of other system load or console activity. Preempt outside Condor jobs to allow local batch jobs to run, but dont preempt local jobs for outside work.

5 BBS Policy Requirements Ensure resource availability for both short and long-running jobs Prioritize short batch jobs so that they are never kept waiting by long batch jobs. Prevent long batch jobs from being preempted or starved by short jobs. Never waste resources No idle CPUs when jobs are waiting to run! No preemption of vanilla jobs! Preemption ideal if you can checkpoint, but here we cant…

6 A Contradiction! No way to guarantee resource availability for short or long jobs without reserving some CPUs for each…...But no way to avoid idle CPUs without allowing them to start any kind of job: If CPUs reserved for short jobs are used for long jobs, they become unavailable to run short jobs. If CPUs reserved for short jobs are not used for long jobs, theyre being wasted when there are no short jobs to run. What to do, what to do…

7 A Solution! Allow resources to be temporarily overcommitted We treat one CPU as two… On a two-CPU machine, define four Condor VMs (virtual machines): two for short jobs and two for long jobs. Allow jobs to be suspended rather than preempted Think of as checkpointing to swap… OR allow jobs to be de-prioritized temporarily If memory is adequate, allow suspended long jobs to continue running at a poor OS priority and steal cycles whenever active short jobs are busy doing I/O.

8 Everybody wins! Short jobs start right away on dedicated short VMs Long jobs arent preempted by short jobs, but rather suspend temporarily or run at a lower priority. Outside jobs run only when no Bologna jobs waiting. All CPUs available to all types of jobs. No idle CPUs when jobs are waiting.

9 Okay, how? Flipside of flexibility is complexity! Its pretty cool that Condor allows you to combine dedicated and opportunistic scheduling in one system, but it takes a bit of work to get it all set up… Luckily for yall, weve already done the hard part, and now you can copy it.

10 Copy it from where? Bologna Batch System document A detailed walk-through of the specific policies and the necessary Condor configuration to make each one work. Line by line examples of how we implemented each. Whats in it? Lets take a look…

11 First Step: No hand waving!! Bologna Batch Jobs are specially-designated jobs which may run only on specially- designated Bologna Batch Servers. Only users in Bologna may submit Bologna Batch Jobs. Bologna Batch Jobs must be vanilla-universe jobs (and therefore are not capable of checkpointing and resuming), and thus once they start they must not be preempted for other jobs. Bologna Batch Servers prefer Bologna Batch Jobs over other Condor jobs, and will start Bologna Batch Jobs regardless of system load or console activity. There are two types of Bologna Batch Jobs, short-running and long-running. Bologna Batch Jobs are assumed to be short-running unless they are explicitly labeled as long-running when they are submitted. A short-running Bologna Batch Job must not be forced to wait for the completion of a long-running Bologna Batch Job before starting. When short and long-running Bologna Batch Jobs are running simultaneously on the same physical machine, the short-running job processes should run at a lower (better) OS priority than the long-running jobs. A short-running Bologna Batch Job may only run for one hour, after which point it should be killed and removed from the queue. Bologna Batch Jobs have priority over other Condor jobs. This means two things: other jobs must never preempt Bologna Batch Jobs, and Bologna Batch Jobs must always immediately preempt other jobs.

12 Review… Job Requirements Machine START PREEMPT RANK WANT_SUSPEND, … JOB_RENICE_INCREMENT PREEMPTION_REQUIREMENTS STARTD_EXPRS, SUBMIT_EXPRS

13 Requirement #1, Bologna Batch Jobs are specially-designated jobs which may run only on specially-designated Bologna Batch Servers.: To identify the servers, place into local condor config: BolognaBatchServer = True STARTD_EXPRS = $(STARTD_EXPRS) BolognaBatchServer To indentify Bologna Batch Jobs by inserting the following line into their job submit description files: +BolognaBatchJob = True Now Bologna Batch Jobs and Servers can identify one another, users ensure that Bologna Batch Jobs run only on Bologna Batch Servers by specifying a job requirement: Requirements = (BolognaBatchServer == True)

14 Requirement #2, Only users in Bologna may submit Bologna Batch Jobs.: Each Bologna Batch Server double-checks the origin of a job claiming to be a Bologna Batch Job : IsBBJob = ( TARGET.BolognaBatchJob =?= True \ && TARGET.SUBMIT_SITE_DOMAIN == $(SUBMIT_SITE_DOMAIN) ) SUBMIT_SITE_DOMAIN is an attribute that INFN defines on all machines, and which they previously configured the Condor schedd to automatically add to each jobs classad. Individual Condor users are not able to override it: SUBMIT_SITE_DOMAIN = "$(UID_DOMAIN)" SUBMIT_EXPRS = $(SUBMIT_EXPRS) SUBMIT_SITE_DOMAIN

15 Requirement #3, BB Jobs must be vanilla-universe jobs, and thus once they start they must not be preempted Next we modified each Bologna Batch Servers WANT_SUSPEND_VANILLA and PREEMPT expressions, which Condor uses to decide when to suspend or preempt a vanilla job, so that INFNs default preemption policy would only affect non-Bologna Batch Jobs. : IsNotBBJob = ( $(IsBBJob) =!= True ) WANT_SUSPEND_VANILLA = ( $(IsNotBBJob) && ($(WANT_SUSPEND_VANILLA)) ) PREEMPT = ( $(IsNotBBJob) && ($(PREEMPT)) )

16 Requirement #4, Bologna Batch Servers prefer Bologna Batch Jobs over other Condor jobs, and will start Bologna Batch Jobs regardless of system load or console activity RANK = $(IsBBJob) INFN_START = ( (LoadAvg - CondorLoadAvg) < 0.3 \ && KeyboardIdle > (15 * 60) \ && TotalCondorLoadAvg <= 1.0 ) START = ( $(IsBBJob) || ($(INFN_START)) )

17 Requirement #5, There are two types of Bologna Batch Jobs, short-running and long-running. Bologna Batch Jobs are assumed to be short-running unless they are explicitly labeled as long-running when they are submitted. Declare long running jobs by placing the following into submit file: +LongRunningJob = True The in the config file, take advantage of meta- operators: IsLongBBJob = ( $(IsBBJob) && TARGET.LongRunningJob =?= True ) IsShortBBJob = ( $(IsBBJob) && TARGET.LongRunningJob =!= True )

18 Requirement #6, A short-running Bologna Batch Job must not be forced to wait for the completion of a long-running Bologna Batch Job before starting.. Declare more Virtual Machines than there are actual CPUs (dual CPU = 2 short VMs, 4 long): NUM_SHORT_RUNNING_VMS = 2 IsShortRunningVM = (VirtualMachineID <= $(NUM_SHORT_RUNNING_VMS)) IsLongRunningVM = (VirtualMachineID > $(NUM_SHORT_RUNNING_VMS)) Change the start expression: SHORT_RUNNING_VM_START = ( $(IsShortBBJob) \ || ( $(IsNotBBJob) && $(INFN_START) ) ) LONG_RUNNING_VM_START = $(IsLongBBJob) START = ( ( $(IsShortRunningVM) && $(SHORT_RUNNING_VM_START) ) \ || ( $(IsLongRunningVM) && $(LONG_RUNNING_VM_START) ) )

19 Requirement #7, When short and long- running BB Jobs are running simultaneously on the same physical machine, the short- running job processes should run at a lower (better) OS priority JOB_RENICE_INCREMENT = ( 5 + ( 10 * ( LongRunningJob =?= True \ || BolognaBatchJob =!= True ) ) If LongRunningJob is true in the job classad, the expression evaluates to (5 + (10 * 1)), or 15. If LongRunningJob is undefined or false in the job classad, but BolognaBatchJob is true, the expression evaluates to (5 + (10 * 0)), or 5. If neither is defined, the expression evaluates to (5 + (10 * 1)), or 15

20 Requirement #8, A short-running Bologna Batch Job may only run for one hour, after which point it should be killed and removed from the queue. Declare long running jobs by placing the following into submit file: PREEMPT = ( ( $(IsNotBBJob) && ($(PREEMPT)) ) \ || ( $(IsShortBBJob) && ($(ActivityTimer) > 60*60) ) ) SHORT_RUNNING_VM_START = (( $(IsShortBBJob) \ && (RemoteWallClockTime<60*60) =!= False) \ || ( $(IsNotBBJob) && ($(INFN_START)) ) ) To remove from the queue, in the job ad add: Periodic_Remove = ( LongRunningJob =!= True \ && (RemoteWallClockTime < 60*60) )

21 Requirement #9, Bologna Batch Jobs have priority over other Condor jobs: other jobs must never preempt BBJobs, and BB Jobs must always immediately preempt other jobs.. RANK already dealt with, now priority preemption: INFN_PREEMPTION_REQUIREMENTS = ( $(StateTimer) > (2 * (60 * 60)) \ && RemoteUserPrio > SubmittorPrio * 1.2 ) PREEMPTION_REQUIREMENTS = \ (( BolognaBatchServer=!=True && $(INFN_PREEMPTION_REQUIREMENTS)) \ || (BolognaBatchServer =?= True \ && ( BolognaBatchJob =!= True \ && ( TARGET.BolognaBatchJob =?= True \ || $(INFN_PREEMPTION_REQUIREMENTS) ))))

22 Wrap condor_submit to make it easy for users bbs_submit_short / bbs_submit_long #!/bin/sh _CONDOR_APPEND_REQ_VANILLA='(BolognaBatchServer == True)' export _CONDOR_APPEND_REQ_VANILLA condor_submit -a '+BolognaBatchJob = True' \ -a 'should_transfer_files = IF_NEEDED' \ -a 'when_to_transfer_output = ON_EXIT' \ -a 'universe = vanilla' \ -a 'periodic_remove = ( LongRunningJob =!= True && (RemoteWallClockTime > 60*60) ) ' \ $*

23 Simple for Users Although policy is complicated, the interface for users is kept simple: Users call bbs_submit_long or bbs_submit_short, just as they would condor_submit… Short jobs start quickly, but those that run for >1 hour are killed. Long jobs will run to completion... bbs_submit_* scripts automatically add the appropriate classad attributes to the job to take advantage of the long or short running VMs on Bologna Batch Servers.

24 Any Questions? me at Check the Bologna Batch System document at Thanks!