4. OCR A Level (H466) SLR1 - 1.1 Pipelining

00:06:25
https://www.youtube.com/watch?v=Pk8gpJEWFRc

Resumen

TLDRThe video explores the concept of pipelining in processors, comparing it to the process of writing invitations among three friends to illustrate the efficiency gained through pipelining. In pipelining, various stages of instruction processing such as fetching, decoding, and executing overlap, allowing multiple instructions to be processed simultaneously, thus improving processor performance. However, limitations like branching can reduce the benefits, as instructions may need to be flushed and removed from the pipeline when a branch occurs. Overall, pipelining is a valuable technique that greatly enhances the efficiency of processors by allowing different stages of various instructions to be processed at the same time, utilizing the ALU and other processor resources more effectively and reducing idle times.

Para llevar

  • 💡 Pipelining in processors improves efficiency by overlapping various stages of instruction processing.
  • ⏩ The technique allows simultaneous fetching, decoding, and executing of instructions.
  • 🔄 An analogy of three friends organizing invites illustrates the parallel task benefits of pipelining.
  • 📉 Limitations like 'branching' can require 'flushing' the pipeline, reducing potential gains.
  • ⚙️ Instruction pipelines and arithmetic pipelines serve different processes in pipelining.
  • 🎯 Utilizes processor resources, like ALU, effectively by reducing idle time.
  • 📈 Pipelining is common in modern processors for enhanced performance.
  • 🔄 The flush occurs when pipeline instructions become irrelevant due to branching.
  • 🔍 Programs with fewer branches benefit more from pipelining.
  • 💾 Different parts of instructions are held in separate registers to maximize efficiency.

Cronología

  • 00:00:00 - 00:06:25

    The video explains the concept of pipelining in processors using the analogy of writing and sending invites more efficiently with multiple people involved, drawing parallels to how a processor can perform tasks more efficiently. In processors, pipelining allows multiple instructions to be fetched, decoded, and executed simultaneously, improving performance by making efficient use of the ALU and CPU caches. However, it notes the limitation that programs with many branching instructions may not benefit as much due to the need to flush and start fetching instructions anew when branches occur. It concludes by prompting viewers to consider how processor speed can be further increased.

Mapa mental

Vídeo de preguntas y respuestas

  • What is pipelining in a processor?

    Pipelining is a technique used in processors that allows multiple instruction processes like fetching, decoding, and executing to occur simultaneously, improving efficiency.

  • How does pipelining improve processor efficiency?

    Pipelining allows for simultaneous execution of different instruction stages, utilizing processor resources like ALU more effectively and preventing idle times.

  • What analogy is used to explain pipelining?

    An analogy of three friends writing, stamping, and addressing party invites is used to explain pipelining, where multiple tasks are done in parallel, speeding up the process.

  • What happens without pipelining in processors?

    Without pipelining, stages like fetch, decode, and execute would occur sequentially, leading to idle times for different processor components and slower performance.

  • What are the types of pipelines mentioned?

    The video mentions instruction pipelines and arithmetic pipelines. Instruction pipelines deal with stages of an instruction, while arithmetic pipelines handle parts of arithmetic operations.

  • What is a major limitation of pipelining?

    A major limitation is branching; if an instruction causes a branch, the pipeline may need to be flushed, as future instructions being processed might become irrelevant.

  • What is 'flushing the pipe'?

    Flushing the pipe occurs when instructions in the pipeline become irrelevant due to branching, requiring those instructions to be removed from the pipeline.

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Subtítulos
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Desplazamiento automático:
  • 00:00:00
    in this video we take a look at the use
  • 00:00:02
    of pipelining in a processor to improve
  • 00:00:04
    efficiency
  • 00:00:08
    [Music]
  • 00:00:12
    okay so to understand this concept let's
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    start by looking at an analogy of
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    writing some invites
  • 00:00:18
    there were three friends that want to
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    organize a party and they want to write
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    and send out invites to 100 people
  • 00:00:26
    so we've got a couple of options here so
  • 00:00:29
    this first option is very inefficient
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    one of the people writes all 100 invites
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    they then Place 100 invites in envelopes
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    and attach the stamp
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    and then they address 100 envelopes
  • 00:00:46
    now obviously with a little bit of help
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    from the friends they can make this
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    process much quicker and more efficient
  • 00:00:53
    so one person starts by writing the
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    first invite
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    while he then starts writing the second
  • 00:01:00
    invite one of his friends places the
  • 00:01:04
    first invite into an envelope and
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    attaches the stamp
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    they then pass that on to another friend
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    who addresses the envelope the second
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    person can now take the second invite
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    and attach a stamp while the original
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    person can start writing the third
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    invite
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    obviously this is a much more efficient
  • 00:01:23
    method and a similar mechanism is
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    effectively what computers use when
  • 00:01:28
    they're doing pipelining
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    so let's have a look at how this
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    pipelining concept can be used to speed
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    up the process of fetching decoding and
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    executing instructions and also discuss
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    one of the main limitations
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    so our processor starts by fetching the
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    first instruction
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    so now we fetch instruction two while
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    instruction 1 moves on and starts to be
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    decoded
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    the processor now fetches instruction
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    three while decoding instruction two and
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    executing instruction one
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    and the process continues the processor
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    fetches instruction 4 while now decoding
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    instruction 3 and executing instruction
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    2.
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    so we can see how pipelining is a
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    technique which can be used by a
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    processor to improve performance but how
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    does it actually achieve this
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    well without pipelining the various
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    different steps within the fetch decode
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    execute cycle would have to take place
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    one after the other
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    in this example we can see that while
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    the next instructor is being fetched the
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    Lu which is responsible for carrying out
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    for mathematical equations is sat idle
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    now this isn't a very efficient use of
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    the Lu or indeed other registers in the
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    processor which may not be involved in
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    the fetch stage
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    by using pipelining the next instruction
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    can be fetched while at the same time
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    the processor is performing arithmetic
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    or logic operations in the ALU for a
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    previous instruction
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    in this way we can make efficient use
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    with the various registers and onboard
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    CPU cache and it allows different parts
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    of instructions across multiple stages
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    to be held in different registers at the
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    same time
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    processor pipelining is often divided
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    into an instruction Pipeline and an
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    arithmetic pipeline the instruction
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    pipeline consists of the various stages
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    and instruction must move through the
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    processor and the arithmetic pipeline
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    consists of the parts of an arithmetic
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    operation that can be broken down and
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    overlapped as They carried out
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    pipelining is very common in today's
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    processors and it allows multiple
  • 00:04:00
    instructions to be executed
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    simultaneously
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    so let's just work through this simple
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    piece of pseudo code on the left
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    well line one has been fetched and we
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    can see that here
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    using pipelining line one now moves on
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    to be decoded while the processor moves
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    on and also which is line two
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    now we fetch instruction three while
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    decoding instruction two and executing
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    instruction one so so far this is all
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    working perfectly fine
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    we now fetch instruction four while
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    decoding instruction three and executing
  • 00:04:51
    instruction two
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    but now potentially we're going to have
  • 00:04:58
    a problem we're fetching in structure
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    five decoding instruction four and we're
  • 00:05:05
    executing instruction three but if you
  • 00:05:08
    notice from our pseudo code instruction
  • 00:05:10
    3 may cause us to Branch elsewhere
  • 00:05:16
    and indeed that's exactly what's
  • 00:05:18
    happened having finally executed
  • 00:05:21
    instruction three we now discover we
  • 00:05:24
    actually need to jump and fetch
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    instruction six
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    and this of course means instruction
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    four and five for which are already
  • 00:05:31
    being fetched and decoded by the other
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    two cores now need to be flushed and
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    removed and this is known as flushing
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    the pipe
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    so while pipelining does indeed improve
  • 00:05:44
    the efficiency of fetching decoding and
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    executing processes a program which
  • 00:05:50
    contains lots of branching instructions
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    may not necessarily benefit much from
  • 00:05:55
    the effects of pipelining
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    so having watched this video you should
  • 00:06:01
    be able to answer the following key
  • 00:06:02
    question how can the speed of a
  • 00:06:04
    processor be increased further
  • 00:06:10
    [Music]
Etiquetas
  • pipelining
  • processor
  • efficiency
  • fetch-decode-execute
  • branching
  • ALU
  • instruction pipeline
  • arithmetic pipeline
  • performance improvement
  • flushing pipe