Re: ext2/3 performance regression in 2.6 vs 2.4 for small interl

[Valdis . Kletnieks]

On Fri, 13 Feb 2004 01:05:20 +0800, Michael Frank said:

> What I am getting at is being annoyed with updatedb ___saturating___ 
> the the disk so easily as the "ancient" method of renicing does not 
> consider the fact that the CPU pwrformance has increased 20-50 fold 
> over disk performace.
> 
> Bottom line: what about assigning "io niceness" to processes, which
> would also help with actively scheduling io toward processes 
> needing it.

The problem is that unlike CPU niceness, where you can literally rip the
CPU away from a hog and give it to some more deserving process, it's not
as easy to rip an active disk I/O away so somebody else can have it.

If the updatedb issues a seek/read combo to the disk, and your process gets
into the I/O queue even 200 nanoseconds later, it *still* has to wait for that
I/O to finish before it can start its seeks and reads.

For an extreme example, consider those IDE interfaces where fixating or
blanking a CD/RW will cause *all* the disks to lock up for the duration.
No matter how high your priority is, you *cant* get that I/O out the door
for the next 60-70 seconds unless you're willing to create a coaster.

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