[PATCH] siimage.c - turning DMA on because of 'md' kernel thread.

From: Kresimir Kukulj (madmax@iskon.hr)
Date: Fri Jul 18 2003 - 17:34:25 EST


        I'm trying to use Sil3112a controller with two Seagate 120Gb SATA
disks for RAID-1 (mirror) with 'md - multiple devices' driver. I am aware
that I need to use some tricks to get it working, like this:

 # hdparm -d1 -X69 /dev/xxx
 # echo "max_kb_per_request:15" > /proc/ide/hd?/settings

First one prevents freezing the system when enabling DMA.
Second one stops IO errors.

As far as I can tell, it works ok, but with reduced bandwidth (because of
max_kb_per_request). When using 'md' driver for RAID-1 mirror (rootfs, swap)
with persistent superblocks I have problems. If server crashes (for some
reason), 'md' tries to resync mirrors automatically. That is done by a kernel
thread that is activated before init(8) is started. I have put 'hdparm' cludge
very early in the boot process, but that happens _after_ 'md' thread starts to
resync. That means that disks are busy (in PIO mode), and when hdparm -d1 -X69
executes, system freezes [if there is no disk/little activity hdparm cludge
passes ok - for example, if RAID-1 is clean so there is no resync].

For past two days I tried to find a way to force ide driver to initialize disk
in dma mode automatically by the kernel itself although disks are set to PIO by
the bios for some reason. I devised a patch that does hdparm + echo cludge. I
have never seen linux kernel, so I am unsure if I did it correctly. Patch is
attached. Please, if anyone uses it, test it to see if it works ok for you! I
am not familiar with linux ide driver so I did this with a lot of printk's and
trial & error.

With this patch, disks are initialized by kernel to UDMA100, with
max_kb_per_request:15. Now, RAID-1 is resynced at boot with DMA already
activated (so there is no need for hdparm) and it completed successfully.
At least it works for me. I need to do more disk stress tests to be sure it is

This is all done with vanilla 2.4.21.
2.4.22-pre4 didn't work at all. Copying a few MB of data freezes the kernel.

My motherboard is Asus P4G8X deluxe.

--- siimage.c.orig Fri Jul 18 23:36:58 2003
+++ siimage.c Fri Jul 18 23:36:59 2003
@@ -97,7 +97,7 @@
         switch(hwif->pci_dev->device) {
                 case PCI_DEVICE_ID_SII_3112:
- return 4;
+ return 3;
                 case PCI_DEVICE_ID_SII_680:
                         if ((scsc & 0x30) == 0x10) /* 133 */
                                 mode = 4;
@@ -297,7 +297,7 @@
         struct hd_driveid *id = drive->id;
         if ((id->capability & 1) != 0 && drive->autodma) {
- if (!(hwif->atapi_dma))
+ if ((hwif->atapi_dma))
                         goto fast_ata_pio;
                 /* Consult the list of known "bad" drives */
                 if (hwif->ide_dma_bad_drive(drive))
@@ -803,7 +803,7 @@
         pci_read_config_dword(dev, PCI_CLASS_REVISION, &class_rev);
         class_rev &= 0xff;
- hwif->rqsize = 128;
+ hwif->rqsize = 15;
         if ((dev->device == PCI_DEVICE_ID_SII_3112) && (!(class_rev)))
                 hwif->rqsize = 16;

I'm confused why is this check there:
         if ((id->capability & 1) != 0 && drive->autodma) {
                 if (!(hwif->atapi_dma))
                         goto fast_ata_pio;

Is it intentional ?

Kresimir Kukulj                      madmax@iskon.hr
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This archive was generated by hypermail 2b29 : Wed Jul 23 2003 - 22:00:36 EST