ICH7: ata_piix twice as fast as ahci?

ICH7: ata_piix twice as fast as ahci?

[Joris]

Hello List,

Odd problem on my machines: the sata disks appear to be a lot slower
when used via ata_piix vs the ahci driver.

* dd if=/dev/sda of=/dev/null runs at roughly 50MB/s under ahci a
steady 100MB/s under ata_piix, same for hdparm
* bonnie++ -d /home/bonnietest -s 16G -r 8192 -u root returns:
** ahci 64bit,16G,70460,99,92676,15,45442,6,66155,94,103556,7,515.9,0,16,4300,16,+++++,+++,2698,9,4735,18,+++++,+++,2611,9
** ata_piix 32bit,16G,50939,99,88159,16,41311,11,38945,69,108351,16,352.9,0,16,5045,5,+++++,+++,3882,4,5099,5,+++++,+++,3489,3

Is this a known issue? Is there a way to diagnose and/or fix this?
I'd love to combine a high-speed system with hotpluggable disks.


Kind regards,
Joris

Extra info:


I tried the following without result:
* The 'raid' functionality was disabled in the bios.
* Update kernels (the debian stable 2.6.18-6-amd64 and 2.6.22-3-amd64
from backports.org)
* Reinstall OS in 32 bit mode
* Limit the amount of ram on the machine to 2GB using the mem=2048M
kernel parameter.


HW info:
Xeon 3210, Supermicro PDSMi+ motherboard, Seagate ES2 500GB sata disks, 8GB ram
Sata controller: 00:1f.2 SATA controller: Intel Corporation 82801GR/GH
(ICH7 Family) Serial ATA Storage Controller AHCI (rev 01)

OS: A bare Debian 4.0 with all security updates, running nothing but
some idle daemons and ssh.

Re: ICH7: ata_piix twice as fast as ahci?

[Alan Cox]

On Sun, 17 Feb 2008 16:41:42 +0100
Joris <joris@v5.be> wrote:

> Hello List,
> 
> Odd problem on my machines: the sata disks appear to be a lot slower
> when used via ata_piix vs the ahci driver.

I would expect that. AHCI allows the use of NCQ and unloads a ton of work
from the processor. It also means you pretty much avoid the inter command
latency that limits standard IDE performance.

Re: ICH7: ata_piix twice as fast as ahci?

[Joris]

2008/2/17, Alan Cox <alan@lxorguk.ukuu.org.uk>:
> On Sun, 17 Feb 2008 16:41:42 +0100
> Joris <joris@v5.be> wrote:
>
> > Hello List,
> >
> > Odd problem on my machines: the sata disks appear to be a lot slower
> > when used via ata_piix vs the ahci driver.
>
> I would expect that. AHCI allows the use of NCQ and unloads a ton of work
> from the processor. It also means you pretty much avoid the inter command
> latency that limits standard IDE performance.

Alan,

>From your response I'm not sure if I made clear that ata_piix was
faster, and ahci slower?

Am I interpreting this correctly as having to choose between fast iops
with low cpu (+ hotplug) with ahci and twice the linear read speed
with ata_piix?



Kind regards,
Joris

Re: ICH7: ata_piix twice as fast as ahci?

[Alan Cox]

> Am I interpreting this correctly as having to choose between fast iops
> with low cpu (+ hotplug) with ahci and twice the linear read speed
> with ata_piix?

Some drives do weird things when NCQ is used and turn off some of their
caching in that case so it depends on the drive what happens to linear
speed.

Alan

Re: ICH7: ata_piix twice as fast as ahci?

[kyle]

Hello Joris,

Have you solve the problem? If so, how? I think I hit the similiar problem
as yours,
but instead of ICH7, I hit the problem with ICH9.

8 x Seagate 500GB harddisks are connected to ICH9 and sil24 PCI-E
controller,
transfer rate of disks connected to ICH9 are limited at around 47MB/s, while
disks connected to sil24 reach 104MB/s. All harddisks are NCQ enabled, so I
don't think NCQ is the problem.

please cc me if possible.

Regards,
Kyle


> Hello List,

> Odd problem on my machines: the sata disks appear to be a lot slower
> when used via ata_piix vs the ahci driver.

> * dd if=/dev/sda of=/dev/null runs at roughly 50MB/s under ahci a
> steady 100MB/s under ata_piix, same for hdparm
> * bonnie++ -d /home/bonnietest -s 16G -r 8192 -u root returns: