Re: DMA transfers in 2.5.67

[mru@users.sourceforge.net (Måns Rullgård)]

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?

I set the latency to 128 using setpci and now I get 66 MB/s.  Other
values give slower transfer rates.  Is there some other setting that
could improve it even more?

-- 
Måns Rullgård
mru@users.sf.net