Mailinglist Archive: opensuse (3175 mails)

[Bill Anderson <bill@xxxxxxxxxxxxxxxxx>]

David Brodbeck wrote:
> Bill Anderson wrote:
>   
> > I noticed that the default elevator applies to everything, including
> > USB memory sticks. I thought the block device driver would change the
> > I/O scheduler to something more appropriate for a memory stick, such
> > as the noop scheduler.
> >     
>
> While we're on the subject, I've also noticed that memory sticks are no
> longer mounted with synchronous writes in 10.2.  I very nearly found
> this out the hard way, by losing data.  I now make sure I issue a 'sync'
> command before unplugging my memory stick.
>
>   
I also noticed this behavior. At one point the default I/O scheduler was 
anticipatory, the current default scheduler is CFQ. I suspect this 
behavior is a result of one of the CFQ parameters, as it keeps thinking 
the memory stick is a disk and attempts to minimize seeks. The resulting 
delay caused by the elevator policy could result in a delay to write 
operations, especially if you were doing a series of reads. With the 
noop scheduler, this behavior disappears as there is attempt to optimize 
seeks. I have to go through the noop code, but I don't think it has a 
bias towards reads over writes. With other I/O schedulers, reads have 
operations have precedence of writes, as long as they don't starve writes.

The documentation on CFQ is very sparse, and a bit dated. Does anyone 
know where I can find current CFQ documentation. I am especially 
interested in documents related to tuning the current version of CFQ.

Bill Anderson
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