[ltp] T21, what ide speed?
Sun, 16 Sep 2001 16:35:05 +0200
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
> 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?
* 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 . Since even my old TP
765L (Pentium 166) is capable of DMA transfers  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think that this discussion is obsolete.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.
 PIO = programmed IO, each byte has to be transfered by the CPU
 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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