Re: DMA transfers in 2.5.67

From: Måns Rullgård (mru@users.sourceforge.net)
Date: Wed Apr 16 2003 - 03:59:43 EST


mru@users.sourceforge.net (Måns Rullgård) writes:

> > > Btw, I just noticed that hard disk throughput is much lower with 2.5
> > > than 2.4. With 2.4.21-pre5 I get ~40 MB/s, but with 2.5.67 the speed
> > > drops to 25-30 MB/s. Everything according to hdparm. Is it possible
> > > that DMA is generally slow for some reason?
> >
> > Possible reason is that in 2.4 we've forced reasonable latency timer
> > value for all PCI devices, while in 2.5 we haven't as yet.
>
> Do you mean whatever causes this message (for a 3com NIC)?
>
> PCI: Setting latency timer of device 00:05.0 to 64
>
> Would that also explain why my hard disks are slow under 2.5? There
> is no corresponding message for the ide controller (htp374).

I just checked the troublesome board. Here's what lspci has to say:

00:06.0 Display controller: 3DLabs GLINT R3 (rev 01)
        Subsystem: 3DLabs: Unknown device 0121
        Flags: bus master, 66Mhz, medium devsel, latency 0, IRQ 27
        Memory at 0000000009020000 (32-bit, non-prefetchable) [size=128K]
        Memory at 000000000c000000 (32-bit, prefetchable) [size=64M]
        Memory at 0000000010000000 (32-bit, prefetchable) [size=64M]
        Expansion ROM at 0000000009060000 [disabled] [size=64K]
        Capabilities: <available only to root>

The latency 0 doesn't look too good. What should I do to change it?

-- 
Måns Rullgård
mru@users.sf.net
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