[rhelv6-list] Performance issues with RHEL6 (iowait)

[John Haxby]

On 9 February 2011 11:05, Matthias Saou <
thias at spam.spam.spam.spam.spam.spam.spam.egg.and.spam.freshrpms.net> wrote:

> Manuel Wolfshant wrote :
>
> > Can you please check that the drives are seen by the system via the SCSI
> > ( as opposed to older PATA ) protocol ? The BIOS must be configured to
> > avoid legacy/compatible mode by all means ( and use AHCI instead )
>
> I'm guessing you're referring to a problem I've indeed seen on some
> similar hardware which had 82801I (ICH9 Family) and where the default I
> saw with RHEL5 was indeed to have the SATA drives appear as hda and hdc
> and resulted in very poor performance. That problem is solved by
> passing hda=noprobe and hdc=noprobe to the kernel. It's not what I'm
> seeing now, where both disks are sda and sdb, and the problem isn't
> that all disk transfers are slow, it's that I/O calls seem to stall
> very often for multiple seconds.
>
>
The disks will be sda and sdb regardless of whether they're connected as
PATA or SATA.  If I was to guess from the information you provided earlier,
I'd say they're connected as PATA.   This being the case, you need to dive
into the BIOS and turn legacy access (or whatever it's called) off and turn
AHCI on.

You can tell which you're using, though, by looking at the output of dmesg |
egrep 'scsi|ata[0-9]':

scsi0 : ahci
scsi1 : ahci
scsi2 : ahci
ata1: SATA max UDMA/133 abar m2048 at 0xf6dfb800 port 0xf6dfb900 irq 43
ata2: DUMMY
ata3: SATA max UDMA/133 abar m2048 at 0xf6dfb800 port 0xf6dfba00 irq 43
ata_piix 0000:00:1f.1: version 2.13
ata_piix 0000:00:1f.1: PCI INT A -> GSI 16 (level, low) -> IRQ 16
ata_piix 0000:00:1f.1: setting latency timer to 64
scsi3 : ata_piix
scsi4 : ata_piix
ata4: PATA max UDMA/100 cmd 0x1f0 ctl 0x3f6 bmdma 0x6fa0 irq 14
ata5: PATA max UDMA/100 cmd 0x170 ctl 0x376 bmdma 0x6fa8 irq 15
ata5: port disabled. ignoring.
ata4.00: ATA-6: ST980815A, 3.ADE, max UDMA/100
ata4.00: 156301488 sectors, multi 8: LBA48
ata4.00: configured for UDMA/100
ata3: SATA link down (SStatus 0 SControl 300)
ata1: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
ata1.00: ATA-8: FUJITSU MHY2120BH, 0085000B, max UDMA/100
ata1.00: 234441648 sectors, multi 8: LBA48 NCQ (depth 31/32), AA
ata1.00: configured for UDMA/100


That's actually my latop which has a SATA disk (ST980815A) and a PATA disk
(MHY2120BH).  The former is (if you work back through the info) attached to
an ahci controller, the latter to an ata_piix controller.  I think your
controllers were using ata_piix drivers which suggests that the BIOS is
being "kind" and presenting you with backwards compatible and slow drivers.

I think my BIOS has all kinds of dire warnings about how your system won't
boot if your switch to AHCI after you've installed an operating system.  By
which, of course, it means Windows which can't cope with the change.

jch
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