file-path:: ../assets/ostep_1680491762166_0.pdf
- virtualization, concurrency, and persistence
ls-type:: annotation
hl-page:: 1
hl-color:: yellow
id:: 642a452b-2dc9-4566-b8a8-95f0caa7b8e3
- didactic 道德说教的；教诲的；
hl-page:: 2
ls-type:: annotation
id:: 642a7c33-ca04-447a-a357-88236d0b9360
hl-color:: green
- Cramming 填塞；填鸭式用功；考试前临时硬记
hl-page:: 3
ls-type:: annotation
id:: 642a80b7-43a1-40ba-ad01-815cb171572f
hl-color:: green
- fond 喜爱（尤指认识已久的人）；喜爱（尤指长期喜爱的事物）
hl-page:: 4
ls-type:: annotation
id:: 642a80ef-5f31-422a-8227-3842faa4eb8d
hl-color:: green
- the operating system as a virtual machine, standard library and resource manager
hl-page:: 25
ls-type:: annotation
id:: 642bb88b-f481-4af6-afb6-7375d37654ce
hl-color:: yellow
- illusion 错觉，幻象
hl-page:: 27
ls-type:: annotation
id:: 642bb978-1efe-418e-8894-8493bfd4f6bb
hl-color:: green
- virtualizing the CPU: run many programs at the same time
hl-page:: 27
ls-type:: annotation
id:: 642bb9c2-efb8-4960-a7bd-36afe1cc0b1d
hl-color:: yellow
- virtualizing memory: each process accesses its own private virtual address space
hl-page:: 29
ls-type:: annotation
id:: 642bbaae-582b-4b1c-bc60-e709931085e7
hl-color:: yellow
- intricate 错综复杂的
ls-type:: annotation
hl-page:: 33
hl-color:: green
id:: 642bbca9-67e2-45d3-a131-968df46c0cef
- heyday 全盛时期
ls-type:: annotation
hl-page:: 39
hl-color:: green
id:: 642bc0e8-ee33-46a6-bf83-407cc1e64737
- incredulous 不肯相信的；不能相信的；表示怀疑的
hl-page:: 45
ls-type:: annotation
id:: 642bc1b3-459e-4e76-b36c-406daba96726
hl-color:: green
- The definition of a process, informally, is quite simple: it is a running program
ls-type:: annotation
hl-page:: 47
hl-color:: yellow
id:: 642bc39c-f56a-488f-a751-1532e413d474
- To implement virtualization of the CPU, low-level machinery and some high-level intelligence.
hl-page:: 47
ls-type:: annotation
id:: 642bc417-a3af-4132-b4b9-9fec9749fc9b
hl-color:: yellow
- mechanisms are low-level methods or protocols that implement a needed piece of functionality
hl-page:: 47
ls-type:: annotation
id:: 642bc41d-8b68-46d9-908e-ab14b53a859b
hl-color:: yellow
- Policies are algorithms for making some kind of decision within the OS
ls-type:: annotation
hl-page:: 48
hl-color:: yellow
id:: 642bc579-a1cc-4b67-a8c5-5a33f274c634
- inventory 库存；财产清单；
hl-page:: 48
ls-type:: annotation
id:: 642bc8a9-1a7d-4236-86ce-65b0498e9e01
hl-color:: green
- three states of a process: Running Ready Blocked
hl-page:: 51
ls-type:: annotation
id:: 642bd104-6b57-44f2-9f10-e5107a926079
hl-color:: yellow
- nitty-gritty 本质；事实真相；实质问题
hl-page:: 55
ls-type:: annotation
id:: 642c279e-0187-4175-abfb-5fcf4e534ae8
hl-color:: green
- KEY PROCESS TERMS
ls-type:: annotation
hl-page:: 56
hl-color:: yellow
id:: 642c27e3-d7d6-41d8-9832-73674615a246
- Interlude: Process API
hl-page:: 60
ls-type:: annotation
id:: 642cc7d2-cd33-4dd6-879f-72f1070ed96d
hl-color:: yellow
Syscall-fork, wait, exec
- Get it right. Neither abstraction nor simplicity is a substitute for getting it right
ls-type:: annotation
hl-page:: 65
hl-color:: yellow
id:: 642cc975-cf26-431c-8c38-617da01d89ee
- the separation of fork() and exec() is essential in shell, because it lets the shell run code after the call to fork() but before the call to exec(); this code can alter the environment of the about-to-be-run program
hl-page:: 65
ls-type:: annotation
id:: 642ccc92-baa5-4b54-8525-9a664698c669
hl-color:: yellow
- imperative 必要的，命令的；必要的事
hl-page:: 67
ls-type:: annotation
id:: 642ccf62-0b5a-41db-899e-3e99a69c2eac
hl-color:: green
- control processes through signal subsystem
hl-page:: 67
ls-type:: annotation
id:: 642cd11a-eea5-48f8-b4d1-b225f37ccdb4
hl-color:: yellow
- Limited Direct Execution: Direct execution is to simply run the program directly on the CPU.
hl-page:: 74
ls-type:: annotation
id:: 642cd1eb-c058-484a-ac25-782e37082bc6
hl-color:: yellow
- aspiring 有追求的，有抱负的
hl-page:: 75
ls-type:: annotation
id:: 642cd2f2-c565-4309-951a-1f809da9beff
hl-color:: green
- user mode and kernel mode
hl-page:: 76
ls-type:: annotation
id:: 642cd3e3-3fa6-43a6-a37a-cae62c634654
hl-color:: yellow
- In user mode, code is restricted in what it can do, otherwise the processor will raise an exception
- User code perform system call to do privileged operation.
- To execute a system call, use `trap` and `return-from-trap` instruction: jump to/from kernel and change the privilege level.
- Limited Direct Execution Protocol-interesting figure illustrating how system call is done
hl-page:: 78
ls-type:: annotation
id:: 642cd6be-083b-4ecd-b220-aafef97a8b65
hl-color:: yellow
- wary 谨慎的；考虑周到的
hl-page:: 79
ls-type:: annotation
id:: 642cd6e9-21fc-49c7-b0bb-0c9ba3b7a524
hl-color:: green
- Switching Between Processes: how OS regain control of the CPU
hl-page:: 80
ls-type:: annotation
id:: 642cd90e-ab6b-4d4d-8312-cd8c69efdac8
hl-color:: yellow
- Cooperative Approach: wait for a system call. 1. The processes are expected to give up the CPU periodically through system call `yield`(which does nothing except to transfer control to the OS). 2. The process does something that causes a trap
- Non-Cooperative Approach: timer interrupt.
- Context switch: save a few register values for the currently-executing process.
Two types of register saves/restores: TI, hardware save state to kernel stack; context switch, OS save kernel registers and restore everything to return from trap
- malfeasance 渎职；不正当行为
hl-page:: 81
ls-type:: annotation
id:: 642cdc2e-329c-423e-a65a-0a53fb6eaa76
hl-color:: green
- scoff 嘲笑；愚弄；笑柄
hl-page:: 83
ls-type:: annotation
id:: 642ce319-8087-4252-b51d-42f749f7c283
hl-color:: green
- enact 制定(法律)；通过(法案)
ls-type:: annotation
hl-page:: 83
hl-color:: green
id:: 642ce357-9914-417b-8036-35ae44ac7283
- whet 引起,刺激(食欲、欲望、兴趣等)
hl-page:: 84
ls-type:: annotation
id:: 642cef47-0c2f-482f-8b61-9a715e5438e5
hl-color:: green
- analogous 相似的,可比拟的
ls-type:: annotation
hl-page:: 86
hl-color:: green
id:: 642cf0c1-59a2-410e-8f45-517f66ef47f9
- workload assumptions: Each job, runs for the same amount of time, arrives at the same time, runs to completion, uses only CPU, and run-time is known
hl-page:: 90
ls-type:: annotation
id:: 642cf292-4464-4c8f-8639-3a194484d4c0
hl-color:: yellow
- Quite unrealistic, but modern preemptive scheduling somewhat mimics part of these assumptions
- scheduling metric: turnaround time, aka `completion - arrival`
hl-page:: 91
ls-type:: annotation
id:: 642cf48d-b312-4af1-a2ff-d55cf9f32e48
hl-color:: yellow
- conundrum 谜,猜不透的难题,难答的问题
ls-type:: annotation
hl-page:: 91
hl-color:: green
id:: 642cf4c4-d246-48f2-a6ef-f14c77684ad9
- First In, First Out (FIFO/FCFS) algorithm
hl-page:: 91
ls-type:: annotation
id:: 642cf4f9-4afd-4240-ac76-5522285fa1eb
hl-color:: yellow
- Bad average turnaround when long job runs first(The jobs run for **different amount of time**)
- Convoy effect: a number of relatively-short potential consumers of a resource get queued behind a heavyweight resource consumer
- Shortest Job First(SJF)
hl-page:: 93
ls-type:: annotation
id:: 642cf705-4a47-4daa-a542-43c4ae6f239e
hl-color:: yellow
- assuming that jobs all arriving at the same time, it could be proven that SJF is indeed an optimal scheduling algorithm
- Downgrade to the same problem of Convey Effect when jobs **don't arrive at the same time**. For example, short jobs arrive shortly after the long job.
- Shortest Time-to-Completion First (STCF)
ls-type:: annotation
hl-page:: 94
hl-color:: yellow
id:: 642cfce4-67f5-4315-bf81-445922b8ae54
- Basically, it is SJF(by our definition is a non-preemptive scheduler) with **preemption**. When a new job enters the system, STCF schedules to the job with the least time left among all present jobs(including the new guy).
- Metric: Response Time. Defined as `resp = firstrun - arrival`. Compare to ((642cf48d-b312-4af1-a2ff-d55cf9f32e48))
hl-page:: 95
ls-type:: annotation
id:: 642e41ac-3b8f-4fe3-a9ef-e2adeeadfe9d
hl-color:: yellow
- For this metric, STCF is not that good.
- Round-Robin (RR)
ls-type:: annotation
hl-page:: 96
hl-color:: yellow
id:: 642e435d-7116-4d2c-9ec3-889558ba2dca
- Not run jobs to completion But run a job for a time slice and then Switch to the next job in the run queue. Repeat until the jobs are done
- Good for Response Time, bad for Turnaround Time.
- Length of time slice is critical, in theory the shorter the better performance under response time metric. However, cost of context switching will dominate overall performance. The cost of context switching comes not only from save/restore registers, but also from caches or something alike.
- amortization 分期偿还；折旧；（均摊）
hl-page:: 97
ls-type:: annotation
id:: 642e4473-4162-4320-91af-fba22e79be25
hl-color:: green
- pessimal 最差的；最坏的
ls-type:: annotation
hl-page:: 97
hl-color:: green
id:: 642e4a5d-37c1-4484-b2ac-913e40d8a2dc
- Incorporating I/O: Overlap. Basic idea is to treat each CPU burst(rather than the whole job) as a job, so that the job is divided into parts. This enables the scheduler to choose another job to run when the job is doing IO
hl-page:: 98
ls-type:: annotation
id:: 642e4ed2-7674-4a5f-bb65-67541b97db95
hl-color:: yellow
- Multi-level Feedback Queue (MLFQ)
ls-type:: annotation
hl-page:: 103
hl-color:: yellow
id:: 642e5117-90c3-41db-9f15-45f3ba9edf91
- Workload: a mix of interactive jobs that are short-running, and some longer-running “CPU-bound” jobs
- Basic rules: each job assigned to a priority level and MLFQ decides which job to run by priority. In this scheme, a job with higher priority runs first, and jobs with the same priority RR. ((642ecc9e-b28b-4951-aaf6-1191e867b34f))
- Change priority: set priority based on its observed behavior, for example, keep high priority for interactive jobs which frequently relinquish CPU.
collapsed:: true
- one of the major goals of the algorithm: It doesn’t know whether a job will be short or job, it first assumes it might be short, thus giving high priority. If it actually is short, it will run quickly and complete; if it is not, it will slowly move down the queues, and thus soon prove itself to be a long-running more batch-like process.
hl-page:: 107
ls-type:: annotation
id:: 642ece05-2fa8-4a24-88e2-f2550cfdd2ed
hl-color:: yellow
- Approximates SJF
- Basic rules for MLFQ:
hl-page:: 104
ls-type:: annotation
id:: 642ecc9e-b28b-4951-aaf6-1191e867b34f
hl-color:: yellow
collapsed:: true
- Rule 1: If Priority(A) > Priority(B), A runs (B doesn’t).
- Rule 2: If Priority(A) = Priority(B), A & B run in RR.
- Problematic priority adjustment algorithm
hl-page:: 105
ls-type:: annotation
id:: 642ecd09-c81b-4127-8bfa-e1fbb78ba583
hl-color:: yellow
collapsed:: true
- Rule 3: When a job enters the system, it is placed at the highest priority (the topmost queue).
- Rule 4a: If a job uses up an entire time slice while running, its priority is reduced.
id:: 642ecd25-c824-4dcd-9a6a-43a717dd5b1e
Rule 4b: If a job gives up the CPU before the time slice is up, it stays at the same priority level.
- Problem 1: starvation.
id:: 642ecd3f-c076-42f1-ba24-7f363eba9e14
If there are too many interactive jobs *occupying the CPU in combination*, then the long jobs will never get to run
- Problem 2: game the scheduler.
For example, a CPU-bound job intentionally issue a trivial IO request just before its time slice is over, so that it will not be moved to lower queue although it should be.
- Problem 3: program behavior change.
id:: 642ed383-c27c-401c-b77f-66e7ec60ba5e
- The Priority Boost
ls-type:: annotation
hl-page:: 109
hl-color:: yellow
id:: 642ed47c-9ba8-4451-b6b3-6ca6ee1dbdda
collapsed:: true
- Rule 5: After some time period `S`, move all the jobs in the system to the topmost queue.
- This solves the problem of ((642ecd3f-c076-42f1-ba24-7f363eba9e14)) and ((642ed383-c27c-401c-b77f-66e7ec60ba5e)). Since the priorities will get recalculated periodically, the scheduler re-learns the jobs' traits which may have changed.
- However, how to choose such `S` is a problem.
- voo-doo constants
ls-type:: annotation
hl-page:: 109
hl-color:: yellow
id:: 642ed799-d933-441a-a043-06e47877c0d9
- Better Accounting
ls-type:: annotation
hl-page:: 110
hl-color:: yellow
id:: 642ed5f6-2a74-4a24-9f69-a472cf644fc9
collapsed:: true
- Rule 4: Once a job uses up its time allotment at a given level (regardless of how many times it has given up the CPU), its priority is reduced.
- This substitutes ((642ecd25-c824-4dcd-9a6a-43a717dd5b1e))
- parameterized scheduler
hl-page:: 110
ls-type:: annotation
id:: 642ed6a2-c04b-4f03-a86f-1d70933c0d42
hl-color:: yellow
- relinquish 交出，让给；放弃
hl-page:: 105
ls-type:: annotation
id:: 642ec9be-dd64-4a66-ab7a-3f0ee376e055
hl-color:: green
- culprit 犯人，罪犯；被控犯罪的人
ls-type:: annotation
hl-page:: 110
hl-color:: green
id:: 642ed5fe-3314-4020-a4fc-b1b75ea987b9
- Proportional-share(fair-share) scheduler
hl-page:: 115
ls-type:: annotation
id:: 642eda22-bd34-42e4-b7e4-1107636d1fbc
hl-color:: yellow
- Instead of optimizing for turnaround or response time, the scheduler tries to guarantee that each job obtain a certain percentage of CPU time.
- tickets: represent the share of a resource that a process should receive
hl-page:: 115
ls-type:: annotation
id:: 642edaa2-78d2-4fde-8b14-584b7d39fa24
hl-color:: yellow
- ticket currency: kind of user interface. Users allocate tickets freely to their own processes, and the system converts user tickets to global tickets according to some kind of exchange rate, in order to achieve fairness between users.
hl-page:: 117
ls-type:: annotation
id:: 642edc09-1329-4eca-95ad-7f62b48875e2
hl-color:: yellow
- ticket transfer: kind of cooperation between processes. A process temporarily hands off its tickets to another process.
hl-page:: 117
ls-type:: annotation
id:: 642edc0f-464d-4616-9313-92b640cecec5
hl-color:: yellow
- ticket inflation: another kind of cooperation. A process can temporarily raise or lower the number of tickets it owns, to indicate that it needs CPU.
hl-page:: 117
ls-type:: annotation
id:: 642edc14-74d6-4758-a21f-d615d2ee51c9
hl-color:: yellow
- Lottery scheduling
hl-page:: 115
ls-type:: annotation
id:: 642edb1d-7740-4459-bb42-0c6a84156475
hl-color:: yellow
- Scheduler **randomly** pick a winning ticket(i.e. number the tickets 1-N, and do a range random), the job which holdes this ticket runs. The more tickets a job holds, the higher chance it is chosen to run. Thus the CPU is shared by proportion, probabilistically.
- Lottery Fairness Study: When the job length is not very long, unfairness can be quite severe. Only as the jobs run for a significant number of time slices does the lottery scheduler approach the desired outcome.
ls-type:: annotation
hl-page:: 119
hl-color:: yellow
id:: 642eded0-39d0-40aa-8b28-c273d39f90c2
- Stride scheduling: a **deterministic** fair-share scheduler.
hl-page:: 120
ls-type:: annotation
id:: 642edf4f-7c7f-477f-acae-0969da13731e
hl-color:: yellow
- Each job has a *stride*, which is inverse in proportion to the tickets it has (conceptually like reciprocal).
Every time a process runs, increase its counter(called its *pass* value) by 1 stride.
The scheduler picks the process with lowest pass value to run
- Why still lottery scheduling? No global states! Thus much easier to implement.
- Problem: How to determine how many tickets to assign to your processes with different purposes and traits? MLFQ does this automatically, but here nobody does this.
- Completely Fair Scheduler (CFS)
ls-type:: annotation
hl-page:: 121
hl-color:: yellow
id:: 642ee1b9-281d-4589-ab90-e776507dd04f
- Goal: to fairly divide a CPU evenly among all competing processes.
hl-page:: 122
ls-type:: annotation
id:: 642ee242-d382-4685-86b4-b3169fcc4fcf
hl-color:: yellow
- virtual runtime: As each process runs, it accumulates `vruntime`. And the scheduler picks the lowest one to run.
hl-page:: 122
ls-type:: annotation
id:: 642ee25b-1f3a-4b7c-a721-fa60f5fa5d2f
hl-color:: yellow
- For blocked processes: need to alter `vruntime` of a job when it wakes up. Otherwise, its `vruntime` would be too small thus breaking fairness. CFS chooses the minimum `vruntime` in the running process table.
hl-page:: 125
ls-type:: annotation
id:: 642ee7e4-20d2-44d5-8407-288a8a2e1769
hl-color:: yellow
- Parameters
- `sched_latency`: when running, scheduler divides this value by the number of running processes `n`. The result is used as the time slice for each process. This simple approach is adaptive to dynamic change of running processes.
hl-page:: 122
ls-type:: annotation
id:: 642ee303-c289-4e55-a0c5-bc4f534fa882
hl-color:: yellow
- `min_granularity`: minimum of time slice, to avoid reducing performance too much
hl-page:: 122
ls-type:: annotation
id:: 642ee3d6-827b-4d80-b6c3-9cb8253a16d6
hl-color:: yellow
- Weighting (Niceness): every process is assigned to a `nice` value ranging from -20 to 19. The smaller nice value, the higher priority. A nice value is mapped to some `weight` through a carefully built table.
hl-page:: 123
ls-type:: annotation
id:: 642ee44f-5fca-4d7d-b688-ff4ac22be23a
hl-color:: yellow
- Given the weight, the time slice can be calculated, and the calculation for `vruntime` needs adaptation to guarantee the time slice.
$$ time\_slice_k = \frac{weight_k}{\sum weight_i}\cdot sched\_latency \\ vruntime_i = vruntime_i + \frac{weight_0}{weight_i} \cdot runtime_i$$
-
- hallmark 特征；特点:
ls-type:: annotation
hl-page:: 126
hl-color:: green
id:: 642ee5dd-9183-4122-9dee-06ff7fb9be46
- panacea 万能药
hl-page:: 126
ls-type:: annotation
id:: 642ee8c2-89fe-4e7b-bf6d-bb0e379f8fe2
hl-color:: green
- remedy 补救方法
ls-type:: annotation
hl-page:: 129
hl-color:: green
id:: 642eeb3a-8803-4c73-84a7-cc48c903f10f
- proliferation 涌现；增殖
ls-type:: annotation
hl-page:: 129
hl-color:: green
id:: 642eeb44-cf62-4cf6-81cb-f1f6423cb66d
- cache coherence
ls-type:: annotation
hl-page:: 132
hl-color:: yellow
id:: 642eecc1-d07d-4e48-bcd5-b84db831b241