[ltp] T21, what ide speed?

[Tino Keitel]

On Sunday, 16. September 2001 15:14, ben knight wrote:
> > I am just wondering at what speeds you operate your IDE busses in the
> > T21. By default even linux-2.4.9 selects idebus=33. I have experimented
> > with appending "idebus=66" to the kernel commandline and so far it seems
> > to work with that speed too. I have not done any elaborate performance
> > comparisions. At idebus=66 setting I get:
> >
> >   [root@blackbox baiti]# hdparm -tT /dev/hda
> >
> > /dev/hda:
> >  Timing buffer-cache reads:   128 MB in  0.99 seconds =129.29 MB/sec
> >  Timing buffered disk reads:  64 MB in  4.05 seconds = 15.80 MB/sec
>
> On an A21, without the idebus=66, thus with the standard 33MHz, I get
> the following:
>
> leeloo:/home/bkk# hdparm -tT /dev/hda
>
> /dev/hda:
>  Timing buffer-cache reads:   128 MB in  0.99 seconds =129.29 MB/sec
>  Timing buffered disk reads:  64 MB in  4.09 seconds = 15.65 MB/sec
>
> Perhaps the thinkpad hardware doesn't support the 66MHz, so ignores it?

>From /usr/src/linux/drivers/ide/ide.c:

	 * ide_system_bus_speed() returns what we think is the system VESA/PCI
	 * bus speed (in MHz).  This is used for calculating interface PIO timings.

The idebus=xx parameter only affects PIO transfers [1]. Since even my old TP 
765L (Pentium 166) is capable of DMA transfers [2] over the IDE interface, I 
think that this discussion is obsolete.

The -T parameter of hdparm has nothing to do with the hard disk. It is 
just a test to find out the speed of the buffer cache in the linux kernel 
without disk access.

[1] PIO = programmed IO, each byte has to be transfered by the CPU

[2] DMA = direct memory access, data from the IDE interface can be directly 
copied into the RAM with no help of the CPU

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