Kbob wrote:
> I can't answer all your questions, but I can tell you how
> to learn what DMA mode Linux is using. Use the dmesg command
> to display your console boot messages, and search for "UDMA"
> in those messages. For example, I see this on tivopc.
>
> > [bmiller@tivopc latest]$ dmesg | grep ^hd.:
> > hda: QUANTUM FIREBALLlct15 30, ATA DISK drive
> > hdb: IBM-DTLA-305040, ATA DISK drive
> > hdc: LTN301, ATAPI CD/DVD-ROM drive
> > hde: WDC WD800JB-00CRA1, ATA DISK drive
> > hdg: WDC WD800JB-00CRA1, ATA DISK drive
> > hda: 58633344 sectors (30020 MB) w/418KiB Cache, CHS=58168/16/63, UDMA(66)
> > hdb: 80418240 sectors (41174 MB) w/380KiB Cache, CHS=79780/16/63, UDMA(100)
> > hde: 156301488 sectors (80026 MB) w/8192KiB Cache, CHS=155061/16/63, UDMA(100)
> > hdg: 156301488 sectors (80026 MB) w/8192KiB Cache, CHS=155061/16/63, UDMA(100)
>
> So three of the disks are in UDMA 100 mode, and one is in UDMA 66.
Here is my dmesg:
Uniform Multi-Platform E-IDE driver Revision: 6.31
ide: Assuming 66MHz system bus speed for PIO modes
PIIX4: IDE controller on PCI bus 00 dev f9
PIIX4: chipset revision 2
PIIX4: not 100% native mode: will probe irqs later
ide0: BM-DMA at 0xffa0-0xffa7, BIOS settings: hda:DMA, hdb:DMA
ide1: BM-DMA at 0xffa8-0xffaf, BIOS settings: hdc:DMA, hdd:pio
hda: WDC WD400BB-53CLB0, ATA DISK drive
hdb: WDC WD400BB-00CFC0, ATA DISK drive
hdc: CD-W516EB, ATAPI CD/DVD-ROM drive
ide0 at 0x1f0-0x1f7,0x3f6 on irq 14
ide1 at 0x170-0x177,0x376 on irq 15
blk: queue c03c0004, I/O limit 4095Mb (mask 0xffffffff)
blk: queue c03c0004, I/O limit 4095Mb (mask 0xffffffff)
hda: 78165360 sectors (40021 MB) w/2048KiB Cache, CHS=4865/255/63, UDMA(100)
blk: queue c03c0140, I/O limit 4095Mb (mask 0xffffffff)
blk: queue c03c0140, I/O limit 4095Mb (mask 0xffffffff)
hdb: 78165360 sectors (40021 MB) w/2048KiB Cache, CHS=4865/255/63, UDMA(100)
I believe the UDMA(100) lines are simply reporting what the drive
says it is capable of. If you look at the top you can see that the
Linux ide driver is using UDMA(66). You can set this by adding
idebus=66 or idebus=100 to your lilo or grub kernel image line,
the default is UDMA(33) if you don't specify anything.
I also believe that the standard Linux 2.4.x kernel (shipping with
Debian 3.0 stable and Red Hat 8.0) does not support UDMA-100, only
UDMA-66, because when I tried specifying idebus=100 I was told that
my kernel image did not support this and would need to be
recompiled to include it.
Anyway, what I was looking for was the DMA mode (0-5) and the PIO
mode (0-4), described under the -X option of hdparm in the manual.
I want to know which mode Linux uses so I tell my BIOS to set the
drives to that mode on startup. My BIOS sets the drives to PIO
mode 3 and UDMA mode 5 if I pick AUTO. But I can override this
if the Linux Kernel is expecting/requiring something else.
Dex
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