A Comparison of Scheduling Latency in Linux, PREEMPT_RT, and LITMUS RT. Felipe Cerqueira and Björn Brandenburg
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1 A Comparison of Scheduling Latency in Linux, PREEMPT_RT, and LITMUS RT Felipe Cerqueira and Björn Brandenburg July 9th,
2 Linux as a Real-Time OS 2
3 Linux as a Real-Time OS Optimizing system responsiveness 3
4 Linux as a Real-Time OS Optimizing system responsiveness PREEMPT_RT (Linux) 4
5 Linux as a Real-Time OS Optimizing system responsiveness Algorithmic changes based on real-time systems research PREEMPT_RT (Linux) 5
6 Linux as a Real-Time OS Optimizing system responsiveness Algorithmic changes based on real-time systems research PREEMPT_RT (Linux) 6
7 PREEMPT_RT Main real-time branch of Linux Goal: decrease scheduling latency through the use of low-level hacks Convert in-kernel spinlocks into (preemptable) mutexes Limit the extent of non-preemptable sections Commonly evaluated with cyclictest Single, easy-to-compare measure of scheduling latency as output 7
8 Testbed for applied real-time systems research Goal Allow implementation and evaluation of novel multiprocessor schedulers and synchronization protocols NOT to reduce scheduling latency Evaluated with Feather-Trace Flexible, fine-grained measurement of different overheads 8
9 Testbed for applied real-time systems research Goal How do LITMUS RT and PREEMPT_RT compare? Allow implementation and evaluation of novel multiprocessor schedulers and synchronization protocols NOT to reduce scheduling latency Evaluated with Feather-Trace Flexible, fine-grained measurement of different overheads 9
10 Testbed for applied real-time systems research Goal How do LITMUS RT and PREEMPT_RT compare? Allow implementation and evaluation of novel multiprocessor schedulers and synchronization protocols NOT to reduce scheduling latency It is not straightforward to Evaluated with Feather-Trace compare them! Flexible, fine-grained measurement of different overheads 10
11 Objective vs. PREEMPT_RT (Linux) Direct comparison of scheduling latency between LITMUS RT and PREEMPT_RT 11
12 Background 12
13 How is LITMUS RT evaluated? Evaluated with Lightweight tracing framework for measuring fine-grained overheads (e.g., IPI latency, context-switching overhead, etc.) Extensively used (20+ publications) Suitable for schedulability analysis Check if a task is going to miss a deadline 13
14 How is PREEMPT_RT evaluated? Evaluated with cyclictest Standard benchmark for assessing real-time responsiveness Creator: Thomas Gleixner Current maintainer: Clark Williams Reports scheduling latency as a single measure Treats hardware and OS as a black-box 14
15 Scheduling Latency Time until the highest-priority task is scheduled brake sensor HP task interrupt! ECU! ISR called 15
16 Scheduling Latency Time until the highest-priority task is scheduled interrupt! wake up task Z Z Z Z T T T! s ISR called scheduler invoked 16
17 Scheduling Latency Time until the highest-priority task is scheduled interrupt! wake up task T T T! s P ISR called scheduler invoked task picked 17
18 Scheduling Latency Time until the highest-priority task is scheduled interrupt! wake up task T T T Perform context switch! s P C ISR called scheduler invoked task picked switched 18
19 Scheduling Latency Time until the highest-priority task is scheduled interrupt! wake up task T T T Perform context switch scheduling latency! s P C ISR called scheduler invoked task picked switched 19
20 How does cyclictest measure Scheduling Latency? Init Measure Exit 20
21 How does cyclictest measure Scheduling Latency? POSIX sched_setscheduler( ) Init Measure Exit Measuring thread is granted real-time status. 21
22 How does cyclictest measure Scheduling Latency? Init Measure Exit 22
23 How does cyclictest measure Scheduling Latency? Init Measure Exit Periodically setup one-shot timers with nanosleep. Calculate delta between the instant the task starts executing and the instant the timer should have fired. 23
24 How does cyclictest measure Scheduling Latency? Init Measure Exit 24
25 How does cyclictest measure Scheduling Latency? POSIX sched_setscheduler( ) Init Measure Exit Measuring thread returns to best-effort status. 25
26 cyclictest on LITMUS RT Init Measure Exit LITMUS RT does not use POSIX API to setup real-time tasks! 26
27 cyclictest on LITMUS RT Init Measure Exit LITMUS RT does not use POSIX API to setup real-time tasks! cyclictest works, but does not measure what we expect... 27
28 Porting cyclictest to LITMUS RT POSIX sched_setscheduler( ) POSIX sched_setscheduler( ) Init Measure Exit LITMUS RT does not use POSIX API to setup real-time tasks! cyclictest works, but does not measure what we expect... 28
29 Porting cyclictest to LITMUS RT POSIX sched_setscheduler( ) POSIX sched_setscheduler( ) Init Measure Exit LITMUS RT does not use POSIX API to setup real-time tasks! cyclictest works, but does not measure what we expect... 29
30 Porting cyclictest to LITMUS RT LITMUS RT API task_mode() LITMUS RT API task_mode() LITMUS RT Init Measure LITMUS RT Exit No changes in the measurement phase, no bias. 30
31 Study 31
32 Questions that We Address Stock Linux Userspace Scheduler + Dispatcher Linux (core) 32
33 Questions that We Address Stock Linux Userspace Scheduler + Dispatcher Linux (core) 32
34 The Cost of LITMUS RT LITMUS RT Stock Linux Userspace Scheduler + Dispatcher Linux (core) Userspace Scheduling Policy Plugins Dispatcher Linux (core) 33
35 The Cost of LITMUS RT LITMUS RT Stock Linux Userspace Scheduler + Dispatcher Linux (core) Userspace Scheduling Policy Plugins Dispatcher Linux (core) Question 1 How much latency does the scheduling policy interface add to the system? 34
36 LITMUS RT vs. PREEMPT_RT LITMUS RT Stock Linux Userspace Scheduler + Dispatcher Linux (core) Userspace Scheduling Policy Plugins Dispatcher Linux (core) PREEMPT_RT Userspace Scheduler + Dispatcher Linux (core) 35
37 LITMUS RT vs. PREEMPT_RT LITMUS RT Stock Linux Userspace Scheduler + Dispatcher Linux (core) Userspace Scheduling Policy Plugins Dispatcher Linux (core) PREEMPT_RT Userspace Scheduler + Dispatcher Linux (core) 36
38 LITMUS RT vs. PREEMPT_RT LITMUS RT Stock Linux Userspace Scheduler + Dispatcher Linux (core) Userspace Scheduling Policy Plugins Dispatcher Linux (core) PREEMPT_RT Userspace Scheduler + Dispatcher Linux (core) 36
39 LITMUS RT vs. PREEMPT_RT LITMUS RT Question 2 What is the penalty for LITMUS RT not being based on PREEMPT_RT? Userspace Scheduling Policy Plugins Dispatcher Linux (core) PREEMPT_RT Userspace Scheduler + Dispatcher Linux (core) 37
40 Evaluation Userspace Scheduler + Dispatcher Linux (core) 38
41 Evaluation Userspace Scheduler + Dispatcher Linux (core) 38
42 Evaluation cyclictest background Userspace + workload Scheduler + Dispatcher Linux (core) 39
43 Background Workloads NO background tasks CPU-bound background tasks I/O-bound background tasks 40
44 Experimental Setup Different kernels: 1.LITMUS RT (Linux 3.0) Partitioned Fixed Priority (P-FP), Partitioned EDF with synchronization support (PSN-EDF), Global EDF with synchronization support (GSN-EDF) 2.PREEMPT_RT (Linux ) 3.Unpatched Linux 3.0 and Linux } SCHED_FIFO 41
45 Experimental Setup 16-core Intel Xeon platform cyclictest s standard setup: one real-time task per processor periods: {1000, 1500, 2000,...} μs Duration: 20 minutes per experiment Almost 6 million samples for each case Results shown in microseconds 42
46 First Scenario NO background tasks 43
47 No Background Tasks Scheduling Latency (!s) 20 Average (99% conf.) Maximum P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 44
48 No Background Similar max. and Tasks avg. latency for Linux 3.0 and LITMUS RT. Scheduling Latency (!s) 20 Average (99% conf.) Maximum P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 45
49 No Background Similar max. and Tasks avg. latency for Linux 3.0 and LITMUS RT. Improved max. latency for PREEMPT_RT Scheduling Latency (!s) 20 Average (99% conf.) Maximum P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 46
50 Second Scenario CPU-bound background tasks Tasks running an infinite loop accessing memory (read/write) Working set larger than L2 cache size 47
51 Second Scenario CPU-bound background tasks Tasks running an infinite loop accessing memory (read/write) Working set larger than L2 cache size Generates memory traffic and cache contention! 48
52 CPU-bound Background Tasks Scheduling Latency (!s) 80 Average (99% conf.) 72.7 Maximum P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 49
53 CPU-bound Background Tasks Scheduling Latency (!s) Average (99% conf.) Maximum Latency under PREEMPT_RT is significantly lower P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 50
54 CPU-bound Background Tasks LITMUS RT s latency lower than on Linux 3.0? Scheduling Latency (!s) Average (99% conf.) 72.7 Maximum Latency under PREEMPT_RT is significantly lower P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 51
55 LITMUS RT vs. Linux 3.0:! CPU-bound Background Tasks log scale! number of samples 1e+07 1e Linux 3.0: scheduling latency (CPU-bound bg tasks) Linux 3.0 P-FP(LITMUS min=2.04us max=72.73us avg=4.22us median=3.86us stdev=1.37us RT ) avg=4.22!s max=72.73!s avg=5.17!s max=47.59!s samples: total= Scheduling Latency (!s) (Bin size = 1!s) overhead in microseconds (bin size = 1.00us) 52
56 LITMUS RT vs. Linux 3.0:! CPU-bound Background Tasks number of samples 1e+07 1e Linux 3.0: scheduling latency (CPU-bound bg tasks) Linux 3.0 P-FP(LITMUS min=2.04us max=72.73us avg=4.22us median=3.86us stdev=1.37us RT ) avg=4.22!s max=72.73!s avg=5.17!s max=47.59!s samples: total= samples out of ~6 million Scheduling Latency (!s) (Bin size = 1!s) overhead in microseconds (bin size = 1.00us) 53
57 LITMUS RT vs. Linux 3.0:! CPU-bound Background Tasks number of samples 1e+07 1e Linux 3.0: scheduling latency (CPU-bound bg tasks) Linux 3.0 P-FP(LITMUS min=2.04us max=72.73us avg=4.22us median=3.86us stdev=1.37us RT ) avg=4.22!s max=72.73!s avg=5.17!s max=47.59!s Slightly worse latencies on average Scheduling Latency (!s) (Bin size = 1!s) overhead in microseconds (bin size = 1.00us) samples: total=
58 LITMUS RT vs. Linux 3.0:! CPU-bound Background Tasks number of samples 1e+07 1e Linux 3.0: scheduling latency (CPU-bound bg tasks) Linux 3.0 P-FP(LITMUS min=2.04us max=72.73us avg=4.22us median=3.86us stdev=1.37us RT ) avg=4.22!s max=72.73!s avg=5.17!s max=47.59!s Scheduling Latency (!s) (Bin size = 1!s) overhead in microseconds (bin size = 1.00us) samples: total= extra spinlock lack of low-level optimizations 55
59 CPU-bound Background Tasks LITMUS RT incurs slightly Scheduling more latency Latency (!s) than 80Linux 3.0 on average Average (99% conf.) 72.7 Maximum Latency under PREEMPT_RT is significantly lower P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 56
60 Third Scenario I/O-bound background tasks hackbench: Linux scheduler stress tool bonnie++: Disk and file system benchmark wget: Network activity 57
61 Third Scenario I/O-bound background tasks Causes a lot of system calls and interrupts hackbench: Linux scheduler stress tool bonnie++: Disk and file system benchmark wget: Network activity 58
62 I/O-bound Background Tasks log scale! Scheduling Latency (!s) 10, Average (99% conf.) Maximum 1, P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 59
63 Huge impact on I/O-bound Background scheduling Tasks latency under standard Linux. Scheduling Latency (!s) Average (99% conf.) Maximum 10, , P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 60
64 Huge impact on I/O-bound Background scheduling Tasks latency under standard Linux. Scheduling Latency (!s) Average (99% conf.) Maximum 10, ,000 PREEMPT_RT is not affected by the interrupt load! P-FP (LITMUS^RT) Linux 3.0 PREEMPT_RT 61
65 Summary 1.Cost of the scheduling plugin layer 2.LITMUS RT vs. PREEMPT_RT 62
66 Summary 1.Cost of the scheduling plugin layer The overhead introduced by LITMUS RT is small 2.LITMUS RT vs. PREEMPT_RT 63
67 Summary 1.Cost of the scheduling plugin layer The overhead introduced by LITMUS RT is small 2.LITMUS RT vs. PREEMPT_RT PREEMPT_RT significantly decreases scheduling latency. 64
68 Importance of Feather-Trace cyclictest was ported to LITMUS RT. Should it become the standard tool for evaluating LITMUS RT? 65
69 Importance of Feather-Trace cyclictest was ported to LITMUS RT. Should it become the standard tool for evaluating LITMUS RT? NO! 66
70 Interference? OOPS... a higher priority task interrupt! wake up task T T T! s ISR called scheduler invoked 67
71 Interference? interrupt! wake up task T T T! s? ISR called scheduler invoked another task picked 68
72 Interference? interrupt! wake up task T T T! s?... P ISR called scheduler invoked another task picked task picked 69
73 Interference? interrupt! wake up task T This length of this interval depends on the execution of other tasks... T T! s?... P ISR called scheduler invoked another task picked task picked 70
74 Interference?..., which depends on other kinds of overhead, preemptions, context switches, etc. interrupt! wake up task T This length of this interval depends on the execution of other tasks... T T! s?... P ISR called scheduler invoked another task picked task picked 71
75 Interference?..., which depends on other kinds of overhead, preemptions, context switches, etc. interrupt! wake up task This length of this interval depends on the execution of other tasks... T T T Overhead-aware schedulability analysis is required!! s?... P ISR called scheduler invoked another task picked task picked 72
76 cyclictest or Feather-Trace? BOTH! cyclictest LITMUS RT /Feather-Trace Practical, easy-tounderstand measure Can easily compare responsiveness between kernels. For tasks other than the highest-priority ones, schedulability analysis is necessary. Only with Feather-Trace we obtain the data required for the analysis. 73
77 Conclusion LITMUS RT : small overheads in comparison with stock Linux PREEMPT_RT is highly necessary for Linux as a RTOS LITMUS RT will be ported to PREEMPT_RT soon Scheduling latency should not be used as the sole metric for quantifying real-time guarantees 74
78 Thank You! We also have a patch that implements Feather-Trace on top of standard Linux, enabling fine-grained measurements. 75
79 Appendix 76
80 Linux 3.0 vs. Linux
81 No Background Tasks Scheduling Latency (!s) Average Maximum Linux 3.0 Linux
82 No Background Tasks Scheduling Latency (!s) 25 Average Maximum 20 Similar averages Linux 3.0 Linux
83 No Background Tasks number of samples number of samples 1e+07 1e e+07 1e Linux 3.0 Linux 3.0: scheduling latency (no bg tasks) min=1.87us max=13.89us avg=2.89us median=2.77us stdev=0.51us avg=2.89!s max=13.89!s Linux samples: total= Linux : scheduling latency (no bg tasks) min=1.52us overhead max=19.73us in microseconds avg=2.89us (bin median=2.58us size = 1.00us) stdev=0.69us avg=2.89!s max=19.73!s samples: total= Similar shapes
84 CPU-bound Background Tasks Scheduling Latency (!s) Average Maximum Linux 3.0 Linux
85 CPU-bound Background Tasks Scheduling Latency (!s) Similar averages 40 Average Maximum Linux 3.0 Linux
86 CPU-bound Background Tasks number of samples number of samples 1e+07 1e e+07 1e Linux 3.0 Linux 3.0: scheduling latency (CPU-bound bg tasks) min=2.04us max=72.73us avg=4.22us median=3.86us stdev=1.37us avg=4.22!s max=72.73!s Linux samples: total= Linux : scheduling latency (CPU-bound bg tasks) min=2.14us overhead max=64.47us in microseconds avg=4.02us (bin median=3.67us size = 1.00us) stdev=1.20us avg=4.02!s max=64.47!s samples: total= Similar shapes
87 I/O-bound Background Tasks log scale! Scheduling Latency (!s) 10, Average Maximum , Linux 3.0 Linux
88 I/O-bound Background Tasks Scheduling Latency (!s) 10, ,000 Similar averages 100 Average Maximum Linux 3.0 Linux
89 I/O-bound Background Tasks number of samples number of samples 1e+07 1e e+07 1e Linux 3.0 Linux 3.0: scheduling latency (IO-bound bg tasks) min=1.85us max= us avg=6.39us median=4.98us stdev=13.25us avg=6.39!s max= !s Linux samples: total= Linux : scheduling latency (IO-bound bg tasks) min=1.85us max= us overhead in microseconds avg=6.23us (bin median=4.60us size = 1.00us) stdev=15.91us avg=6.23!s max= !s samples: total= Similar shapes
90 LITMUS RT s plugins 87
91 No Background Tasks Scheduling Latency (!s) Average 26.2 Maximum P-FP PSN-EDF GSN-EDF 88
92 No Background Tasks Similar shapes 1e+07 1e LITMUS^RT G-EDF: scheduling latency (no bg tasks) min=1.59us max=14.34us avg=3.06us median=2.56us stdev=1.18us 1e+07 samples: total= e number of samples LITMUS^RT P-EDF: scheduling latency (no bg tasks) min=1.76us max=26.17us avg=3.45us median=2.87us stdev=1.24us overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FPlatency (no bg tasks) min=1.96us max=15.13us avg=3.45us median=3.10us stdev=1.03us number of samples GSN-EDF avg=3.06!s max=14.34!s 1e+07 1e avg=3.45!s max=15.13!s samples: total= overhead in microseconds (bin size = 1.00us) PSN-EDF avg=3.45!s max=26.17!s samples: total=
93 No Background Tasks Similar shapes 1e+07 1e LITMUS^RT G-EDF: scheduling latency (no bg tasks) min=1.59us max=14.34us avg=3.06us median=2.56us stdev=1.18us 1e+07 samples: total= e+06 number of samples LITMUS^RT P-EDF: scheduling latency (no bg tasks) min=1.76us max=26.17us avg=3.45us median=2.87us stdev=1.24us overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FPlatency (no bg tasks) min=1.96us max=15.13us avg=3.45us median=3.10us stdev=1.03us number of samples GSN-EDF avg=3.06!s max=14.34!s 1e+07 1e avg=3.45!s max=15.13!s samples: total= overhead in microseconds (bin size = 1.00us) PSN-EDF avg=3.45!s max=26.17!s 2 samples samples: total=
94 CPU-bound Background Tasks Scheduling Latency (!s) 80 Average 73.3 Maximum P-FP PSN-EDF GSN-EDF 91
95 CPU-bound Background Tasks 1e+07 1e LITMUS^RT G-EDF: scheduling latency (CPU-bound bg tasks) min=1.91us max=60.20us avg=5.81us median=5.39us stdev=2.51us samples: total= e+07 1e+06 number of samples LITMUS^RT P-EDF: scheduling latency (CPU-bound bg tasks) min=2.40us max=73.27us avg=5.14us median=4.21us stdev=2.95us samples: total= overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FP latency (CPU-bound bg tasks) min=2.10us max=47.59us avg=5.17us median=4.37us stdev=2.75us number of samples GSN-EDF avg=5.81!s max=60.20!s 1e+07 1e avg=5.17!s max=47.59!s overhead in microseconds (bin size = 1.00us) samples: total= PSN-EDF avg=5.14!s max=73.27!s Similar shapes 92
96 CPU-bound Background Tasks 1e+07 1e LITMUS^RT G-EDF: scheduling latency (CPU-bound bg tasks) min=1.91us max=60.20us avg=5.81us median=5.39us stdev=2.51us samples: total= e+07 1e+06 number of samples LITMUS^RT P-EDF: scheduling latency (CPU-bound bg tasks) min=2.40us max=73.27us avg=5.14us median=4.21us stdev=2.95us samples: total= samples overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FP latency (CPU-bound bg tasks) min=2.10us max=47.59us avg=5.17us median=4.37us stdev=2.75us number of samples GSN-EDF avg=5.81!s max=60.20!s 1e+07 1e avg=5.17!s max=47.59!s overhead in microseconds (bin size = 1.00us) samples: total= PSN-EDF avg=5.14!s max=73.27!s Similar shapes 93
97 I/O-bound Background Tasks log scale! Scheduling Latency (!s) 10, Average Maximum , P-FP PSN-EDF GSN-EDF 94
98 I/O-bound Background Tasks Scheduling Latency (!s) 10, Similar results 1,000for P-FP and PSN-EDF 100 Average Maximum P-FP PSN-EDF GSN-EDF 95
99 I/O-bound Background Tasks Scheduling Latency (!s) 10, Similar results 1,000for P-FP and PSN-EDF 100 Average Maximum Higher average for GSN-EDF P-FP PSN-EDF GSN-EDF 96
100 I/O-bound Background Tasks 1e+07 1e LITMUS^RT G-EDF: scheduling latency (IO-bound bg tasks) min=2.26us max= us avg=10.95us median=7.38us stdev=14.11us 1e+07 samples: total= e number of samples LITMUS^RT P-EDF: scheduling latency (IO-bound bg tasks) min=1.98us max= us avg=6.56us median=5.11us stdev=12.66us overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FP latency (IO-bound bg tasks) min=1.89us max= us avg=6.60us median=5.17us stdev=12.76us number of samples GSN-EDF avg=10.95!s max= !s 1e+07 1e avg=6.60!s max= !s overhead in microseconds (bin size = 1.00us) samples: total= PSN-EDF avg=6.56!s max= !s samples: total= Similar shapes 97
101 I/O-bound Background Tasks 1e+07 1e LITMUS^RT G-EDF: scheduling latency (IO-bound bg tasks) min=2.26us max= us avg=10.95us median=7.38us stdev=14.11us 1e+07 samples: total= e number of samples LITMUS^RT P-EDF: scheduling latency (IO-bound bg tasks) min=1.98us max= us avg=6.56us median=5.11us stdev=12.66us overhead in microseconds (bin size = 1.00us) overhead in microseconds (bin size = 1.00us) LITMUS^RT P-FP: scheduling P-FP latency (IO-bound bg tasks) min=1.89us max= us avg=6.60us median=5.17us stdev=12.76us number of samples GSN-EDF avg=10.95!s max= !s Higher average 1e+07 1e avg=6.60!s max= !s overhead in microseconds (bin size = 1.00us) samples: total= PSN-EDF avg=6.56!s max= !s samples: total= Similar shapes 98
102 threadirqs in Linux
103 No Background Tasks number of samples number of samples Linux threadirqs Linux : scheduling latency (no bg tasks) min=1.60us max=25.15us avg=2.82us median=2.65us stdev=0.47us avg=2.82!s max=25.15!s 1e+07 samples: total= e Linux : scheduling Linux latency (no bg tasks) min=1.52us overhead max=19.73us in microseconds avg=2.89us (bin median=2.58us size = 1.00us) stdev=0.69us avg=2.89!s max=19.73!s 1e+07 samples: total= e
104 CPU-bound Background Tasks number of samples number of samples 1e+07 1e e+07 1e Linux threadirqs Linux : scheduling latency (CPU-bound bg tasks) min=1.95us max=40.90us avg=3.67us median=3.29us stdev=1.19us avg=3.67!s max=40.90!s Linux samples: total= Linux : scheduling latency (CPU-bound bg tasks) min=2.14us overhead max=64.47us in microseconds avg=4.02us (bin median=3.67us size = 1.00us) stdev=1.20us avg=4.02!s max=64.47!s samples: total=
105 I/O-bound Background Tasks number of samples number of samples 1e+07 1e e+07 1e Linux threadirqs Linux : scheduling latency (IO-bound bg tasks) min=1.51us max= us avg=5.89us median=4.67us stdev=14.33us avg=5.89!s max= !s Linux samples: total= Linux : scheduling latency (IO-bound bg tasks) min=1.85us max= us overhead in microseconds avg=6.23us (bin median=4.60us size = 1.00us) stdev=15.91us avg=6.23!s max= !s samples: total=
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