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72linus

Member

From: gordonsville,va

Registered: 2009-03-14

Posts: 144

Website

cfq vs bfq vs ?

I was wonderin whats the big difference between I/O schedulers cfq and bfq?
is it that bfq is for SSD devices and cfq for all hard drives or what?

or is it that bfq is somehow "better" but in what way?

please in layman's terms explain the differences and does cfq/bfq affect how the user's pc runs, is it noticeable?
thanks

ngoonee

Forum Fellow

From: Between Thailand and Singapore

Registered: 2009-03-17

Posts: 7,362

Re: cfq vs bfq vs ?

http://lmgtfy.com/?q=BFQ+vs+CFQ

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jasonwryan-Installing Arch is a measure of your literacy. Maintaining Arch is a measure of your diligence. Contributing to Arch is a measure of your competence.
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lucke

Member

From: Poland

Registered: 2004-11-30

Posts: 4,019

Re: cfq vs bfq vs ?

http://retis.sssup.it/~fabio/linux/bfq/

ScottArch

Member

From: Cork, Ireland

Registered: 2009-10-23

Posts: 58

Re: cfq vs bfq vs ?

Hi there,

"The time-based allocation of the disk service in CFQ, while having the desirable effect of implicitly charging each application for the seek time it incurs, suffers from unfairness problems also towards processes making the best possible use of the disk bandwidth. In fact, even if the same time slice is assigned to two processes, they may get a different throughput each, as a function of the positions on the disk of their requests. On the contrary, BFQ can provide strong guarantees on bandwidth distribution because the assigned budgets are measured in number of sectors. Moreover, due to its Round Robin policy, CFQ is characterized by an O(N) worst-case delay (jitter) in request completion time, where N is the number of tasks competing for the disk. On the contrary, given the accurate service distribution of the internal WF2Q+ scheduler, BFQ exhibits O(1) delay."

Essentially, it is my understanding that, regardless of medium, BFQ generally performs better (for desktops) were perceived intractability (vs real throughput) is preferred. CFQ may unwittingly (I assume to be applicable to both server and desktop environments) penalise a well written program with fast throughput, in favour of a slower program by virtue of its reliance on allocated 'throughput' vs BFQ's 'time' reliance.

N.B. I may have really missed the point here!

72lius: I took from your question you were asking for user experience with BFQ. Perhaps search for the technicalities of it first, then ask for the user experience angle... To be honest the dull technical articles are often the best place to start (look at the BFQ literature, it's dull, but informative)! Hope tis was considered helpful and not harsh...

N,B. I would like to suggest that Ngoonee's link (http://lmgtfy.com) could become the 'arch' way to address 'searchable' questions, I thought it was hilarious ... and effective

Good luck!

Scott

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Acer Aspire 5920G - 2Ghz Core 2 Duo T7300 - 256mb Nvidia 8600GS - 4GB RAM

Saren

Member

Registered: 2014-04-02

Posts: 13

Re: cfq vs bfq vs ?

Sorry for necrobumping, but I think it's just not cool to reply lmgtfy as answer. It's because this thread is at top result when I searched for "bfq cfq server" on Google.

WorMzy

Administrator

From: Scotland

Registered: 2010-06-16

Posts: 13,572

Website

Re: cfq vs bfq vs ?

Members of this community are expected to do their own research. If this is the top result on google, then that's google's problem, not ours.

You are clearly aware that necrobumping is discouraged, please don't do it again.

Closing.

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Sakura:-
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