[ILUG] Extremely slow/CPU intensive SATA IO on 2 CPU HT server.

[Conor Wynne]

On 12 Mar 2006, at 19:02, David Wilson wrote:

> Hi folks,
>
> We have a dual 2.8ghz Xeon server with 2gb RAM running vanilla  
> 2.6.15.1
> which is seeing some really odd IO behaviour. I've always been aware
> that the machine felt slightly more sluggish than it should have, but
> upon running an extremely simple UPDATE on 80,000 or so rows in
> PostgreSQL last night, the machine crapped itself and jumped to a load
> of 8.0.
>
> For comparison, the same UPDATE runs on the same dataset on the same
> version of PostgreSQL on a single CPU 2.8ghz P4 FreeBSD 4.10  
> machine in
> slightly less time, and not even pushing the load past 0.2.

Cannot really compare against another OS, at least you know the hardware
should handle it.

> The filesystems are ext3.
>
> The load isn't caused by userspace, indeed PostgreSQL sits at 6%
> utilisation for the most part, as the machine load climbs  
> indefinately.

So do you feel its a SATA bug?
If so, have you tried another kernel/driver?

>
> The only thing I can think of is having the hosting company pull up  
> the
> BIOS and turn off hyperthreading, something I've been meaning to do  
> for
> various other reasons anyway.

Try "noht" to disable Hyperthreading in your bootloader.
You may also wish to try "noapic"

>     Linux 2.6.15.1 #1 SMP Fri Jan 20 19:47:58 GMT 2006 i686

You may also wish to see if the issue occurs with a 2.4 kernel.

>     scsi0 : ata_piix
>     ATA: abnormal status 0x7F on port 0xC407
>     ata1: SATA max UDMA/133 cmd 0xC800 ctl 0xC482 bmdma 0xC000 irq 17
>     SCSI device sda: 586072368 512-byte hdwr sectors (300069 MB)
>
> Does anyone have any pointers? Thanks,

When the issue occurs, try running iostat on the device to see if its  
really an I/O issue.

>
>
> David.