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Bug#520928: linux-image-2.6.26-1-686: PIIX4 /dev/hda performance regression (10x times, DMA dissabled)



On Mon, 2009-03-23 at 18:36 +0100, root wrote:
> Package: linux-image-2.6.26-1-686
> Version: 2.6.26-13lenny2
> Severity: important
> 
> 
> I have 450NX server board (two cpu Xeon II 450MHz). My ide controler is PIIX4.
> 
> I found that after update to lenny's 2.6.26-1-xen-686 IDE performance droped
> to just 1.50MB/s (hdparm -t). With 2.6.18-6-xen-686 I had 21.54 MB/s.
> (Tested both in -xen-686 and -686, in signle user). Performance
> of scsi disc's doesn't changed.
[...]
> [    4.054227] piix: 450NX errata present, disabling IDE DMA.
> [    4.054433] piix: A BIOS update may resolve this.
> [    4.056035] PIIX4: IDE controller (0x8086:0x7111 rev 0x01) at  PCI slot 0000:00:0c.1
> [    4.056051] PIIX4: not 100% native mode: will probe irqs later
> [    4.056051] PIIX4: IDE port disabled
> [    4.056051]     ide0: BM-DMA at 0x2c20-0x2c27
> [    4.056757] Probing IDE interface ide0...
> [    4.349476] hda: IBM-DTLA-307030, ATA DISK drive
> [    5.021402] hda: host max PIO4 wanted PIO255(auto-tune) selected PIO4
> [    5.021674] hda: no DMA mode selected
> [    5.021888] hda: host max PIO4 wanted PIO255(auto-tune) selected PIO4
[...]
> So it looks like there is some blacklist (in piix modules) for this server board,
> and kernel uses generic (and non-dma) module for ide. But with 2.6.18-686 it was working.

However, this blacklist has been present since before Linux 2.6.12, so
it doesn't really explain the change.

> Additionally I probably have newset BIOS possible.
> 
> Mayby this is because of broken write cache flushing?
[...]

What do you mean?

> As far as I know rev 03 is blacklisted for some reason. Is there a way to force
> dma?

I expect that you can do this using hdparm, but I wouldn't recommend it.

Ben.

-- 
Ben Hutchings
It is impossible to make anything foolproof because fools are so ingenious.

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