IO Scheduler Diagrams

IO Scheduler Diagrams

[Georg Schönberger]

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Hello,

this topic is not directly connected to Fio but nevertheless reasonable for all Fio Users.
I am currently working on IO Scheduler Diagrams explaining how they process IO requests.

Attached you find my first draft, I've already had some input from Christoph Hellwig. I would be happy
if I get more feedback as I am not sure if everything is correct, especially with CFQ I had some problems drawing it.

-Georg

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Re: IO Scheduler Diagrams

[Jens Axboe]

On 2012-10-05 11:41, Georg Schönberger wrote:
> Hello,
> 
> this topic is not directly connected to Fio but nevertheless reasonable for all Fio Users.
> I am currently working on IO Scheduler Diagrams explaining how they process IO requests.
> 
> Attached you find my first draft, I've already had some input from Christoph Hellwig. I would be happy
> if I get more feedback as I am not sure if everything is correct, especially with CFQ I had some problems drawing it.

Two comments:

- For deadline, the FIFO queues are just for tracking the ordering of
  the requests. They serve no other purpose than to restart the position
  inside the sorted tree (which is a tree, btw, it's not a linked list or
  FIFO as the diagram would lead you to believe).

- For CFQ, the async queues are per-disk and split in prio classes and
  priorities. The sync queues are per-process per-disk. Your graphic
  doesn't really show that, it's a fairly complex relationsship.

-- 
Jens Axboe