Re: Huge iowait on 2.6.4 - not on 2.4.20 !

[Albert Cahalan]

alan pearson writes:

> On 2.6 the iowait jumps to around 70%, while 2.4 on
> both tests it is firmly zero.

The 2.4 kernel lumps iowait into idle, so you
won't see iowait on a 2.4 kernel.

> On disk read, I'm loosing 30 Mb/sec of bandwidth PER
> DISK, compared to 2.4.20.
> I've tried using both the deadline and as ioschedulers
> but no difference.
>
>
> Under real conditions (ie our application running
> which reads from all the disks simultaneously) on
> 2.6.4, the system performance is around 1/3 of 2.4.20)
>
> Summary MB/Sec :
>
>         dd if=x         dd if=/dev/zero
> 2.4     64              35.6
> 2.6     30.34           35.9

Well, that looks serious, but unfortunately you
can't tell what the iowait was on the 2.4 kernel.
Only the 2.6 kernel provides this information.


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